114 is the 6 cyl version
115 is th 5 cyl version

manual box will go straight in - the cutout inn the chassis is the same - as is the pedal box cutouts (clutch hole is there on an auto)

propshafts are diferent - as probably are diffs - but thery are interchangeable as regards bolt holes (very easy job as well - diff held in with iirc 4 bolts from the trunk / boot.

throttle linkage easy. manual has ball joints for take off to gearbox, auto just has them connected. ditto vacuum pipes

as regards flywheels / torque converters - dont know off the top of my head.

late (post 73/4) have ribbed rear light lenses, early have smooth ones. late ones look a bit w123 esque.

advice - take out gearbox, subframe and engine as one. DO NOT TRY TO SEPARATE GEARBOX FROM ENGINE - genuine mb manual states you need 4 feet of extension bars.... technically possible, but not worth it

gearbox lever - lift the carpet where you expect to see the gearlever - is there a plate there? if so - no problem in fitting. if no hole - then im surprised, and i could give you photos / dimentions to help.

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C140 420 CL
W114 280CE pimpmobile
W114 250/8 Hillclimber with M110 and bike carbs - got any hot cams?