engine & gearbox

Are engines more or less married to a gear box, i.e. if you replaced an engine for a different make or model, would you also have to replace the gearbox?

if you stay withing the same family of engines, you could keep the gearbox, but other than that expect to need an adapter plate at least.

Some makes are better at this than others, ie Fords use the same stud pattern for the mating of gearboxes and engines on most (all?) of their transverse mounted engines, and have for years