Can anyone give a quick but well informed answer to this naiive question:
Is the bottom-end of the 750 the same as for the 907? Can I rebuild the heads from the 907ie onto a 750 bottom-end, with all its auxiliary stuff like water pump??

thanks

Easier to get an answer here than hope I get the answer right by inspection / documentation review.

no it`s not.
The 750 is an oil cooled, 5 speed gearbox engine with 88mm pistons, the 907ie is a water cooled, 6 speed gearbox engine with 92mm pistons.
Due to the different gearbox the 907ie engine case is a little wider and the cylinder stud distances are bigger due to the larger pistons. Of course the engine case opening for the cylinders is also larger.

G.