chevyfreak68

my 8.2 went out in my 68 firebird so i swaped it out to a 10 bolt 8.5 posi it had some 208 or something along those lines in it but anyway i had a set of 3.08 so i decided to swap them out iv done this before in my truck changed out a set of gears with out changein shims and it worked fine but this time this thing sounds like a sirin when you do about 60mph what do i need to do and whats the right way? only going to brake it apart one more time ha and if anyone has a set of 3.73 i would be intrested