I plan on doing the same swap some day. I just haven't found the right 240 body yet. I checked into putting a 300 turbo radiator in the 240 already. The oil cooler and hoses are different configurations so that did not work. The turbo motor also has a fan switch on the thermostate housing that will also need to be put into the 240 wiring harnes. The 300 turbo auto trans is different than the 240 completely so you will need a 300 turbo auto tranny to go with your motor. The best way is to have a crashed 300 turbo donor available. Like having a Pick n Pull in your own drive way.

Anyone have a nice 240 Donor in Central California for me?

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)