I was going back and realized I missed page 3 of your thread. I dropped a 5.2 Magnum into my coupe with little to no trouble at all. Currently, I'm installing the PCM and fuse panel from the 2001 Ram donor truck. My suggestion to you would be to find either a 5.2 or 5.9 Magnum to drop in. The scrap yards are full of them. My original 318 was trashed and the magnum cost a lot less than buying an old 318 and rebuilding.You might want to set the 273 in a corner for later. You know good and well that the kid will probably trash the 273 anyhow! LOL
The Magnum engine bolts right in. The 904 and 727 also bolt right on. Pick up the mini starter. They also fit. The LA timing covers will also bolt on. I got engine, fuse panel, PCM, harness, and all bolt on accessories for $400. Great way to go!