XPT

Two labourers on a job site: Laurie, a short Maltese bloke, can carry 8 bricks at a time. His mate, Shane, is a tall beefy Aussie bloke. He can carry 12 at a time. This is torque.
 
Laurie however, is quite athletic and nimble, and is able to shift those 8 bricks from one pile to another 3 times a minute. So he can move 24 bricks in that time. Shane is a bit slower, at only 2 trips, but each load contains more bricks. So Shane can actually move 24 bricks in the same time that Laurie can move 24. This is power.
 
I think we all need to be on the same page when having a discussion about torque and power. XC I think you're referring to two engines of different stroke but with everything completely optimised for their corresponding size. I think everyone else is comparing two engines that are identical in every way except for stroke.
 
The physics dictate that, RPM for RPM, more torque will make more power. In fact, at 5252 rpm, both hp and lb-ft are always identical. So if torque at this rpm is more, so will be the horsepower. So in order for a smaller engine to make the same hp as a bigger one, it must spin faster.
 
The Boss 302, in race form, could put out around 500hp. However it had to rev upwards of 8000 rpm to achieve it. This kind of rpm dictates serious engine prep, an expensive valve train with solid lifters, and an engine that's off its tits.
 
A 393 stroker Clevo could reach this number without cracking 6000 rpm, even using a near-stock valve train and hydraulic lifters. A much easier engine to live with, more mild-mannered and longer-lived.
 
So everybody's right in regard to what they're talking about, but we're not talking about the same thing.

Say you took a Boss 302 , ripped the top end off and bolted it onto a 351W bottom end with the same CR and cam etc. It would not make 1 more HP than the 302?

Yep, Joe Gauci's Corty. What a weapon, I think it's a twin turbo V8 nowadays.

200 turbo cubes right here...
 

Anything you can do to promote flow in any application is a good thing.  More air/fuel in makes for more power, especially when the cam is set to take advantage of it. 
 
It really depends on what you are chasing with the package.  being a 200/ 200 motor it will love to rev and that is a good thing with the boost.  I would suggest an EF crank in there as well to help smooth harmonics tho. 
 
An off the shelf grind may be suitable in a moderate power level, basic set up but really I would be talking to any of the local cam grinders and coming up with something to suit your application. 
 
Obviously BA turbo motors perform very well and I think this is in part due to their better flowing cylinder heads, so a tickle up of your XE head can not hurt performance. 
 
I guess what I am trying to get at is you need to work out what power level you are aiming at, and probably add another 100hp as boost becomes addictive (from everything I have read) and design the package around that application. 
 
In a light xp ute any power you generate will be good fun.  I am aiming for 450@ the wheels for my XM turbo project and I have a ported E2 head here that runs some good numbers.  Ray HALL up here, who is a well renowned turbo man, told be he made over 550 at the wheels from a turbo x-flow in the early 90's.  smart man.  It had a good cylinder head and great tune so I guess the two go hand in hand. 

Well I will be interested in this as well but I would deffinatly look at a custom camshaft for it with wide lobe sep and some lift.Duration isn't needed on a boosted engine but lift and a wide lobe sep helps.The camshaft will only tell the engine WHEN it is going to make it's power and how much to a degree but you don't want close enough you want right so off the shelf is not wanted here.
 
As for the head lets wait and see but you would assume been boosted it will be a case of the turbine will push it in no matter what and tune to suit.That said a bigger inlet and a worked exhaust port as you need exhaust flow to move the turbo could only help here IMO but most likely wrong...LOL     

I reckon a tidy-up of the throat and de-dag of the rest of the port is as far as you should go. Maybe a port-match (can't hurt) Otherwise it will, like you say, be a slug until the turbo comes on. Remember you don't have nice, long runners in your inlet to help with port tuning. Air velocity is the key, so port size needs to be as small as possible, particularly if the engine is 20% smaller than what all the bits were intended for.
 
I'd keep the valves stock size too. I reckon the exhaust port could cop a bit more work as I reckon it needs it. Don't bother with 3-angle valve cuts, etc, especially on the exhaust. You need all the surface area in the seat that you can get to transfer heat out of the valve.
 
Camshafts, I'd go with a towing cam. They come in at about 1800 on a 250 so a 200 might be at 2100 or so. It actually had a towing cam in it (FYI everyone: this donk used to be mine) and that was very torquey if you can remember.

Thanks for the responses guys,
Sly I know what you are saying about cam selection, and from what I understand you don't want too much overlap with a turbo motor. I guess it's all a balancing act. If the ports are too big coupled being 200ci with around 8.5:1 compression and a large turbo (MP T70) it will be a dog off boost. If ports/valves are too small you restrict top end power. This is a grose simplification of course.
 
Ando I hear you with the 4litre EF fully counter weighted crank only problem is it will become a 250 again due to the stroke. The last time I read the RTA rules my car can only be 3 times it's weight in capacity with forced induction. 1170 x 3 = 3510cc maximum capacity that's the reason for going with the 200. Otherwise the extra 50 cubes would be great!
 
I will probably talk to someone like Wade or Camtech for their recommendations if you guys think there isn't an off the shelf mild cam suitable. I'm not going to be running massive boost (1.2 bar max) due to the fact that I'll only be using prepped 200 rods and probably hypatec pistons. Looking at the compressor map my turbo can pump a theoretical 450-500 hp worth of air at 1 bar so if I can make everything work as efficiently as possible hopefully it can make good power.
 
As for power levels I want enough power that the car is fun to drive without doing a 360 every time I put the boot in. So I'm guessing maybe 350-400rwhp. If It did anywhere in the 11's I'd be chuffed.

If only the barra hit that hard hey??? 

Why not just get complete late EL- AU3 XR8 running gear ? They rated from factory 185-220kw (gt40p headed). It's not worth the trouble of fitting the e7 headed 165-175kw Windsor from eb-el xr8 and non XR8 v8s in AU. The e7 heads are not great for performance and the manifolds aren't good either so even fitting them to an earlier block would give disappointing results.
A manual AU setup with a cam and remap would get along nicely in an XF.