W123 manulua trans in a 107
 

Will a 4 speed manual from a 240D 123 bolt up to a 500 v8 from a 1982 500SL? the trans it has now has a 126 part number.

No..completely different bell house.

I don't think the tranny could handle the torque anyway.

Has anyone experimented with adapting a 5 or 6 speed transmission to the 500 V8? maybe a transmission from an american car?

It has been discussed here in the past. Mercedes never made a manual trans for the early V8's. Even if you could find a suitable box, you would be up for a custom adaptor plate, Flywheel and clucth combination grief, pedals, shortened or lengthened/re balanced tail shaft, custom box mount , possible gearbox ratio, diff ratio incompatibility, manual or hydraulic clutch mods and at the end of it, starter motor combinations the list goes on. Even if you can fabricate the bits, you could wind up with a vehicle that drives like a dog due to bad ratio combinations. Modification compliance is an issue here, if it is in the States, you'll have the Wallopers all over you like fleas on a dog for non compliance. Sorry to hit you with so many negatives.
Brian.
280SL Euro
500SEL Euro.