It is physically possibly however you need to do a whole lot of custom work. Someone started a RWD project Trep that ended up on ebay last spring. The rear end was their just needed rear suspension hooked up. He had also used a Chevelle subframe for the rear.
The engine looks like it was just placed in the engine bay for pics, as it wasn't bolted down and the motor wasn't going with the car. I have pics of it if you would like them, I could email them to you.
I've pondered this project many a time. But you will need to cut a channel to fit the driveshaft and a Torqueflight or 904 tranny into the car. Your best bet is to take a 76-80 Plymouth Volare or Dodge Aspen front clip and fabricate it to the front of the trep. Basically its the front clip that almost all hot rodders use to put Mopar power plants in. With that you can fit anything from a 318-360-408 stroker(same physical size as the other two but lots of torque). And if your really daring you can get a set of mounts that will allow you to mount a 440 to the Aspen/Volare front clip. However I don't think it would fit very well in a Trep, but fits nicely in the Aspen and Volare.
**Edit** And there is also a company that has fabricated HEMI-heads for mopar small blocks, comes with everything you need from, complete heads, intake, cam, block hugger headers, and some other goodies. That would be something to see in a trep
Also you will need to change the entire front suspension due to the added weight. And again this is why I say use the Aspen/Volare front clip. Their are heavy duty police car components for it and believe me it makes the car handle great.
Also carburetors are the way to go. Easiest way to change power without hassels of an ECU. And if you want the best carburetor get a Barry Grant Demon carb. I would talk to them before you purchased though because they have different carbs for cam profiles. Unlike Holley's theirs are pretty much for specific applications and not just putting one on different motors because the cfm's are right.
If you lived closer I could let you have a rolling Plymouth Super Coupe(Hi-po Volare) chassis that my Dad and I stripped for parts. Its got a posi 8 3/4" rear end and police suspension all around. I wanted to use the front clip for the Intrepid but my Dad won't let me start another project. But the rolling chassis will go to the scrap yard bare, if no one claims it.