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!

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V