Bag54,
Being that I also have a 54 truck that has been on the road for over 2 years you can feel safe in checking out my Webshots album and saving yourself a bunch of trial and error stuff. I'm running the 62" 88 Camaro drum 3.42 diff and have the correct wheel backspacing both front and rear. One suggestion I'm make would be to stick with the 15X7" rims. Plenty of tire selection and no interference problems with the front (tie rod ends) or rear fenders and box. I'd also suggest considering 235/70 series tires so you can rotate. The 16" rims would look okay but I can't speak to clearance issues with a 50 or 60 series tire. A 28" tall tire is going to fill up the wheel well.
As for the Camaro 62" wide diff, there are plenty of 3.08's out there as well as 3.42's. The 3.08 would probably be a reasonable choice for running behind your stock 350. I first set my truck up with an IROC-Z 3.08 disc/posi. These diffs were made in Australia and should handle the torque from a daily-driver 350...however, the ratchet emergency brake mechanism and lack of replacement axle seals could be a problem. I am not a great fan of power 4 wheel disc brakes in a truck without ABS. Even with an adjustable proportioning valve, the rear brakes were extremely touchy. I now have manual brakes with front discs and rear drums with a 3.42 R&P and find I have much better control over rear-wheel lockup.
Speaking of budgets.....I had no luck in finding 4 decent matching rims in the j-yards with a 5 on 4-3/4" pattern so be aware that you may be springing for new rims. The Camaro diffs sell for $100-150. in this area, but an IROC posi/disc will set you back twice that. When you find your diff be sure to have the yard include the rear sway bar and control links, the emergency brake cables intact, and the driveshaft.
The primary reason I tossed out the info on the 8.8 was for the guys with overdrive transmissions, (.63 OD's) that weren't having any luck finding later model GM 3.73's. They are a couple inches narrower than the GM (Camaro) but that can be compensated for in reducing the backspacing, they are plentiful, easily adaptable, with lower mileage, and relatively inexpensive. Hope this helps.
Dave
