The first place to check is Tom's out of CA,
www.tomsdifferentials.com.
They have been building differentials for years and can certainly handle your requirements. It will cost you a lot but it will be right.
You have a couple of options. First off don't believe the myth that corvettes are different-that usually means the guy doesn't know what he's talking about or they want to jackup the cost to the owner because "vettes are different"
The vette differential ,63-79, isn't much different then a 10 or 12 bolt chevy. It uses a Eaton posi carrier. You can upgrade the posi by first checking its condition. Is the cross pin hole true or egg shaped? Is the cross pin worn a little in the center? What type of gears are in the posi, count the teeth on the side gears and small spider gears you want to use 10-17's. Some places will cold stabilze them for added strength. You can get a shim kit from Tom's to "tune" the posi. This will give much better performance to the posi and eliminate the chatter you get going around corners. Look at the posi clutches stay with the solid type your car probably has the "snowflake" type and will break under heavy load. Replace the bearing caps with steel caps and socket head cap screws. The caps should be setup with a .001 rock so they crush down to prevent the bearing race from spinning. At least change the bolts if not the caps.Deburr and radius the housing and carrier to cut down on spots that could develope a crack. Richmond gears are known for making noise so be aware of that. I've used the US Gears made for Tom's and had very good luck with them.
Doing this should make your diff strong enough for your needs,there's always the 12 bolt retrofit too. You can "shoe horn" a 12 bolt Eaton into the standard vette housing. It requires grinding the housing and turning the ring gear in a lathe but it will hold up to just about anything you put in the eng bay.
Now who can do this work? That something you're going to have to find out in your area. I've spoken to many vette shop owners who don't know about a lot of this because they rebuild stock diff's, a good racing guy could probably do it, or if you've worked on other diff's then do some research and do it yourself? I would ask your guys these questions and see what they say,if they don't know what you're talking about find someone else.
