Help decoding this bell housing !

see the round thing with 4 bolts?

measure that. or get the part number off of it and then match it up here: Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists

the bellhousing and that bearing retainer need to match each other in diameter. early a-body cars used a smaller bellhousing and smaller diameter flywheel, so fitting the later, "larger" bellhousing makes things tight-- hence the advice of maybe needing to flatten out the pinch weld in the tunnel to make everything fit.

anyway short version: trans bearing retainer has to match bell, bell has to match flywheel & clutch.