Just started 66 barracuda- No Drive, No Reverse

If rear Was welded ,probably has blown spiders in center section. What size diff is in it, does it have a rear cover? Pull cover and see what's up
I got up today and checked the fluid with the engine running, added another quart and looked under the car with the trans in neutral and saw that the shaft was spinning but the wheels were on the ground so that's not good. Gonna pull the cover off after work.