rearend question

I bought a 69 barracuda with a 8 3/4 489 case posi . The guy told me it was all rebuilt. After i took it home useing my tow dolly and put it in my garage i started to look the car over and checked the fluid in the rear end and their wasnt any in it (bone dry).
I towed the car about 45 miles didnt really get past 50 mph.
My question is do you think the gears are fine or should i just take it apart and check .
thanks for your oppinions