If you do the swap it will probably be a fun project as you have everything you need on the donor car.

I did a swap many years ago on my e21. Started out as 320 auto with carby, bought a 323i that had been rolled and swapped everything over. Ended up having to do a bit of bodywork too as there were subtle differences between 1977 and 1979 (firewall back a bit and indent for brake powerbooster, exhaust cutout different at rear). The 323i had different brakes, suspension, fuel tank, exhaust, wiring, instrument cluster. In the end, the only original part of the 77 car was the body, but boy was it worth it.

If you are a hands on guy, I say go for it.

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2004 E53 diesel.
Titan silver on black
Sports package