I'm very interested in this possibility as well, but in reverse. I just learned that my 300TD's engine is on it's way to the engine bay in the sky, and therefore I'm taking this opportunity to consider engine swaps with a donor 300E in a few months. How would a 6-cylinder 300E engine fit into a 123 body?

I know to go from diesel to gas I'd need to rig up a whole array of relays and extra fuses for the fuel delivery and injection systems... for your case you'd have to bypass it and let the MFI do work its magic.

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'82 300TD
'77 6.9
'75 280S
'74 280
'87 Porsche 944 turbo