a friend with a good 3.0 diesel engine found a nice 240D w123 bod
y with a 4 speed manual. Will the 3.0 bolt up to the 4 speed?

yes, though the 240 flywheel is not ideal.

Use the search function, there is endless information on this subject.

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1982 300TD 210K miles ("The Replacement" aka "The Anvil") - SOLD
1979 300SD 245K miles (never ending project)
2007 Pinarello F3:13
1995 Ducati 916 (SOLD, sniff)
1999 Ducati 900SSie (SOLD)