Thom

The change in 4.0l happend in mid 98' pre mid 98 4.0 will have a 4E---- or ---DT if tickford number cast into components (easiest ones to pick are cylinder head, timing cover block etc) and will have early style valvetrain (2.1 rocker ratio straight valve springs and lager valve spring retainers) the bottom end will also have crossflow sized main bearings and shorter con rods (than au through barra) late 98 (known as hybrid in el) through au will have a casting numbers starting with WR2A---, the cylinder head has 1.8:1 rocker ratio, beehive valve springs smaller valve stems and smaller valve spring retainers, the bottom end has larger main journal's, longer con rods, a girdle and in au will have an aluminium sump with the main caps cross bolted to the sump, the el hybrid engines are essentially an au engine with a tin sump, xh may have got the update later than the sedans did as xh production happened nearly a full year into au production

Do you have the sandwich plate between the block and the bellhousing, if you don't the starter spacing and position will be incorrect, if you are after a cheap hi torque starter anything from ea to bf falcon will fit crossflow

Xg are different to xf, but you still need an aftermarket sway bar for au 4.0 or barra, AFAIK tuff mounts are the only ones currently doing aftermarket sway bars, like Dean said its a conversion one, if you wanted something heavier you'd probably have to have it made, On the rear you can use a sway bar to suit xd

I've put a couple of hundred au head gaskets on e series falcons (always good to source au spec bolts too), I've always had the head skimmed and just cleaned the block really well with scrapers and an oil stone, as long as the block is flat it will hold up for more than a couple of 100,000ks, its funny most ea to ed head gasket failures I've seen were caused the head gasket failing or corrosion in the head, 7 out of 10 ef/el failures were a broken bolt on cylinder 2 or 5, usually exhaust side

Using a 6 cylinder t5 will mean you have to get a crs bellhousing as the 6 cylinder t5 has a different length input shaft to a v8 one, the diff will be fine and the t5 will hold up reasonably well as long as you don't abuse it ( when I was a p plater I broke many of them with a warmed up 4.0l but they were pretty well abused)

No, do not use oil flush it will cause the same problems dumping kerosene in the sump would, the goal is to clean the engine gently and slowly, anything that rapidly speeds that process up is what causes problems, the only safe way to clean an engine fast is to dissemble it

Safest way to clean it if there's no metal in the filter is to use a higher detergent oil (like a diesel oil) and do 4 or 5 sub 1500km oil changes, it won't make the engine spotless inside but it will clean gradually and shouldn't dislodge anything big enough to cause damage, flushing fresh oil through the engine before firing it up with the new cam won't hurt anything and is a pretty good idea, make sure you use plenty of assembly/ break in lube on the cam and lifters when you install them

Flushing the sludge/ metal from the cam & lifters without pulling the sump/ cylinder head to clean out all the oil galleries and oil pump/ pickup will most likely be a death sentence for that engine, you can guarantee you will loosen and flush a large percentage of the gunk in the engine, but that's not the problem, it's what gets left behind that is now free to roam the engine until finds a nice oil gallery or oil pump pick up or oil return to plug up and cut off the oil supply to that area of the engine. Also if metal has been through the engine the oil pump needs to be inspected as the rotors and oil pressure relief need to be inspected for damage and the pump replaced if they are

Xe and xf stock exhaust centre section is supposed to be 2 inch for all models, with carby engines having a 1.75inch tail pipes and efi crossflows having a 2 inch tail pipe, 2.25 works really well for stock to mild crossflows if you want a little bit of noise without it getting annoying

It's not the "correct way" to do it but I've fitted one with self tappers before, if you wanted to do it a bit better than that I've used nutserts and then bolted it in

I think deans on it, only other thing it could be is a valve not seating

It may have had other problems I wasn't as good with carbs back then, as much as I thought I was at the time, but you can learn a little bit in 15 years, I do remember it making a huge difference to that car at the time, it made as much of an improvement as putting an efi cam in it and swapping the auto for a t5

When I was 19 I had an xf wagon I got from the original owner, it had 60,000ks on it it was a 4.1 and was the slowest car I had ever driven (I even pulled the plugs and measured the stroke to make sure it was a 250 and not a 200) turns out it had a webber from a 3.3 on it previous owner swore black and blue the carb was original to the car, I put a webber off a 250 on it and it made a huge difference

E series a/c compressor doesn't fit au accessory brackets, to swap to e series accessories won't help either, as the a/c compressor is is still too wide with the e series brackets (e series brackets also require a different timing cover, water pump and balancer than au) as dar as running a/c goes you would need to modify the passenger side rail to clear the pump, but if you aren't going to run a/c you can just use a shorter belt and remove the a/c pump all together

Xg or xh pano?, if its xg you have everything l, if its xh you'll need either xg engine mounts or modify some crossflow engine mounts, with either you'll need to modify the radiator mounts to suit the xf core support, you'll probably benefit from swapping the diff out of the donor car too, it isn't quite as simple as I've jut said but if you've changed an engine before it's not much harder, physically bolting running gear in is the easy part, swapping wiring looms, getting a shifter sorted and making the dash work is the hard part and may require a little bit figuring