I have an 86 firebird that originally had the 305 with a 4 barrel. What's the rear end gearing on this. I know it's not posi. I figure my cam would do better with a 3.73 or something along that lines

I think you can trace it through your VIN # - and look on this board for the VIN code breakdowns

My Haynes manual for my 85 Camaro has the axle codes - you just have to look on top the pumpkin or on your passenger side axe tube (don't quote me) for your axle code

If I had a wild guess - 3.08 - for the 305