W126 380SEC vs 500SEC - what are the actual engine differences - thinking about an engine swap project

cant find the old thread.

Got a client looking at a 1983 380SEC. Car is clean. Price is fair. He wants to swap a 500 engine in eventually.

Actual engine differences between the 380 (M116) and the 500 (M117) on the W126 coupe. Are they bolt-in. Is the swap straightforward or a nightmare. Asking because i need to advise the client properly.

I know the 500 is more displacement (5.0 vs 3.8) and more torque. But is it a simple sub or do i need to budget for harnesses ECU gearbox etc

Vasilios is correct.. the economics of the 380-to-500 swap have never made sense. The car you create is a 500SEC with a wrong VIN plate (the M116 chassis plate). The car loses its originality value and gains nothing it could not have had by buying the original..

Tell your client to buy a 500SEC. Or buy a 380SEC and accept it as a 380SEC, which is a fine car in its own right.