Since all 240D's(W123) use a 3.69/1 rear end that won't cause a problem. The drive shaft is longer(front) in the stick shift, but since you have one already that won't be a problem either. The 1980 engine uses pin-style glow plugs so that won't be a problem either. Time to swap parts will be the biggest challenge!! Have fun!
MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V