Slow250XC

Camtech ct-142 503b 110 probably a bit small for your combo but really drivable.
 
I'd lean toward the 517 something to be said for low down torque than outright power

Fuck that........powweeerrererreddrredrr

Should have added already done new valves, springs retainers etc.
And i have been haggling with a supplier over some street terra rockers,
Exhaust is extractors to 2.5 inch pipe,a 2 chamber muffler and out infront of rear wheel so flows pretty well.
Compression ratio as worked out when i did the lpg build was 10.6.
Im a whiskey drinking redneck in the nz countryside, ain't nothin sensible 'round ere haha
 
Happy friday guys, drink up!!!

Here have a crack at this. You'll see what a big cam does to your dynamic compression. Also they have preset values for lots of engines including crossys. http://www.pcengines.com.au/calculators.asp

Crow 650 is going to be much more than just a "freshen up". It's advertised at 292/292 and lobe lift is 0.302" which on a 1.73 rocker gives 0.522" at the valve. Anything much over 0.5" lift, ditch the stock valve train. This cam will need springs, roller rockers and if going stud-mount, guide plates too. True, it has a wide lobe separation but that bleeds compression at low rpm. It will need a decent carb, extractors and exhaust. Also compression will need to go up by 0.5 of a ratio minimum.<br /><br />If you just want a sensible upgrade using stock parts, I'd suggest keeping it close to 0.5" lift with a 602 or 603 grind. These are single pattern, 270 and 280 deg respectively. At 0.050" they are 208 and 214. My first cam was the same as a 602 and it had great torque from 2000-4000. My current one is a 666 (dual pattern 270/280) and despite clevos apparently liking the dual pattern more, I think I took a step backwards with that choice. Anything bigger than the ones I mentioned, you need some serious work to make it come alive.