Flexplate problems with 727TF

I can get the original transmission from the durango pretty cheap ($300) should i just try to fit it to my valiant instead of going the TC route? It will be a 4 speed maybe with OD (IDK) and will hook up to all the computer crap on this new Magnum Computer.. What would yall do? This is from a 42K miles Durango, so I'm feeling good about decent parts.
What problems are waiting for me on the engine and transmission swap?

Drive shaft custom cut? Trans mounting crossmember? Shifter linkage? What else?

I'm really frustrated with this because THIS SITE said the 1999 Magnum would bolt right in. Now I'm looking at months or thousands of dollars to get my car back on the street.