72 340 4 spd question

hi everyone I have a 1972 340 car numbers matching. It is a 4spd and I'm thinking about buying a 4 spd on Craigslist looks complete minus shifter lever and handle. The guy says its off a 360 and maybe barracuda. Because it has a long tailshaft. I was wondering if this would fit my 1972 340 demon? He says the flywheel is for an external balanced 360 would that work for mine? Was a 72 340 internally balanced or external? Or would I need a specific flywheel etc? Let me know please. Thank you