T56 is way fatter than any mopar trans from back in the day. To get that in you will have to cut floor and torsion bar crossmember.

I think the TKO kits that used to be a big thing can go in a factory torsion bar crossmember but in order to clear it the transmission has to sit way too low at the back for a good pinion angle. Floor mods still required and I believe torsion bar crossmember cutting if you really want the transmission to sit right.

If cutting is a problem for you, there's always the OD transmission from Passon that bolt right in.