i just pulled out an original 2.73:1 open centre 7.5 inch rearend from an 82 Z/28
and had a brand new!! 3.08 possi and carrier installed in my old housing
my engine is crankin hard so i needed the better setup,,,,,,,,,,,,,,
i seem to have 2 sepperate wrench kits opperating on this swap over,,,,
the lower arms on the diff seem to take metric wrenches,, while the shocks seem to be imperial nuts on the lower I bolts on the bottom of the shocks,,,,,but metric nuts on the rear ,, some are metric nuts while others are SAE or (standard american engineering) some are 18mm,, some 3/4,, some are 17mm on this swap over , i encountered this metric thing in the engine bay on the 400ci instalation also,,,,,,some parts in the engine bay took metric wrenches to remove,things,,,,,,did these cars have metric bits on them,,,as well as SAE,,,,,i know canada was metric in the 80,s,, so was AUSTRALIA,,,,,(home of the GTO),

 

yes you'll find both. the engine, rear, and maybe trans will be imperial as you call it. the parts attaced to the rear are mostly if not all metric from what i've seen.

 

Yup GMs little practical joke for giggles. You've got metric, standard, & torx bolts to deal with

 

ok i was starting to think some jerk pulled this car apart and lost the original bolts,,,,,,,,,, yep i thought so,,,,,,,,,,wow weird,,,,,