W123- 4spd manual into 300d vs Om617a into 240D

[dinman]

So

I currently have a US spec '83 300d. Wonderful mechanically. Starts up on the first revolution or so, doesn't leak oil, doesn't even really smoke unless it's super cold out and even then it's just a puff on start up. fresh nozzles, glow plugs, etc. Shifts pretty nicely. Pretty horrible cosmetically. Core support/ frame damage from previous owner. Leaks a little water in when raining from a wide array of locations. Bad door seals. A/C system would have to be totally re done (lines leading to nowhere, parts missing, etc). I have been driving the car for two years now and it has been bulletproof after I changed the nozzles, one prechamber, and the glow plugs.

I found a manual 240d for sale not too far from me. Also an '83. Power windows, power sunroof. Manual climate control (which I think I prefer over the auto in my 300)

It is in much, much, much better cosmetic shape than my 300d.

How much trouble is it to swap the om617 from my '83 300d into the '83 240d? More trouble than swapping the trans + all associated parts into the 300d? Or not?