My 1981 380se wont move in first gear but is fine after that, suspect major prob, have been offered a free 116 V8 auto, does anyone know if it is possible to fit? Australia.

Simple answer: No. The bellhousing on the cast iron block V8's in the 116 chassis were much larger than the ones on the aluminum-block V8's in the 126 chassis. Now, whether or not you can adapt a 116 tranny to it with a little work, I'm personally unsure. But I dont think so.

Also, the 116's tranny will only be a 3-speed, yours is probably a 4-speed?

thanks, saves me lots sweat and anguish, and then finding doesn't fit.
3 or 4 speed didnt worry me, better than now with no speed.