Transmission Options?
An A500 from an early 90s Dakota will bolt to your engine and use the same shifter/throttle linkage stuff you have. You will have to cut out part of your torsion bar cross member to make room for the fatter rear end on this trans, fabricate a new cross member/trans mount piece, as well as shorten your driveshaft. No floor pan mods will be needed other than whatever you decide to do for reinforcement above or below the cross member area you cut out. This site has good information on this conversion. This is probably the cheapest way to overdrive your small block mopar.