I've got a spare 8.5 from my 88 c1500 sitting around. I was wondering if I could cut the brackets for the old mounts and weld up new ones if it would work. Has anyone tried this before?

 

The topic has been covered many times, you can get a lot on it from a search.

Basically, no. The tq arm bracket is not welded to anything, it is part of the casting of the housing. - There is no great way to weld to cast to create a bracket either. Unless you are very good a fabricating and welding you will easily tie up as much $ in attempting to swap it as just buying an aftermarket bolt-in rear(12-bolt/60/9"), only to still have stock internals that won't hold much more than the 7.5".

 

There is a LOT of work involved in this swap. The '88 rear end will have 28 spline axles, and probably a Governor Lock. Not the best way to go, but better than the 7.5.

 

I forgot all about the torque arm mount. Guess I'll just use one temporarily for my truck while I'm building up the other.

 

There's also a width factor. Truck diffs are usually a lot wider than a car diff.

 

It will be a lot of fabrication work, but if you're capable of doing it yourself the 8.5 is still a good way to get a strong rear for not a lot of money. The housing will be too wide, so it will need to be narrowed, but when you do that you can also add 9" style housing ends to eliminate the need for c-clips. Some 8.5s had 30 spline axels, so you can buy differentials with 30 splines and I think there may even be aftermarket 33-35 spline ones available. I run 30 spline shafts and an ARB front/Detroit Locker rear in my '87 K5 in the 8.5s and am a firm believer that this is a stout axel. I stayed away from the 1-ton running gear swap and saved myself probably two hundred pounds, a couple inches of ground clearance, and a lot of hassle. My 8.5 are just as strong as stock 1-ton gear, probably stronger.