Hmmm. $3k for the transmission. $800 for a new bellhousing to make it fit. $500 for a clutch to fit the Ford or GM input shaft. $300 or so for another driveshaft because the old one will likely be too long/short. Figuring out some way to run the speedometer. Possible floor modifications because there is NO Mopar application. Hard to claim no floor modifications to a car when there is no application for that transmission in a Mopar. Cutting the floor to put the shifter through since Mopars have the shifter to the side, not straight up the middle.
So you're at $4600 on something that may not fit, doesn't handle a much torque(600 in the Tremec, 700 for the GFI), and a better overdrive in the GFI. Unless you get the .68 GM version.
I'd prefer to spend the extra $1400 and unbolt one and put the other in in a matter of hours using my existing driveshaft and clutch/bell.