Well I ended up removing the diff, not to bad of a job, about 2 hours. I don't think the bolt was tightened all the way because it had some play in it which is evidenced from the oblong hole it left in the bushing and the begining of the housing. Brought the diff up to Vintage Motorsports for there opinion and they said it should be fine. They drilled it out and retapped it for me, thanks again Jay and they're sending me the new bolt.
This is kind of interesting though, since I had the diff out I figured I'd change the gear
oil in it because it doesn't get any easier when its out of the car. I removed the plugs and tipped it upside down over a drain pan and let it sit for about an hour. When I tipped it back over I found the head of a hex bolt with about 1/4" of thread left on it in the drain pan. Its a 10mm hex head. Part of the bolt went through the gears at some point which is evidenced from the jagged end. I removed the back cover to have a better look turned the gears all around but I don't see any obvious damage. Stuck a magnet all around inside but didn't find anything. Its the same size as the two bolts that hold the speedometer sensor in place (which were not missing). Don't know how it got in there but I guess I dodged another bullet with this car. Sure glad I decided to change that fluid.
BTW anybody know where I can order a new gasket for the back cover?