Wilwood offers 2 caliper brackets for the rear disc conversion kit for my 1968 firebird, which will fit?

My 1968 Pontiac Firebird has the original 10 bolt rear end, Wilwood offers a 2.75" offest caliper bracket and a 2.81" caliper bracket and i need to know which kit to order. Apparently, Chevy made 2 different 10 bolt rear ends in 68 and i don't know which kit will fit the one i have, i'd appreciate any help