904 question
depending on the year of the /6 unit it may or may not have kickdown/passing gear.
what "guts" are you looking to swap? because if it's seals and o-rings and clutches i don't think i'd trust that stuff that's been sitting around.
if you're doing a rebuild and you're just taking some hard parts to replace some stuff that's worn or out of spec and refreshing all the soft parts i don't see a problem with intermingling.