The ring gears for pre-engaged and inertia starters have a different tooh count, even though you can sort of get away with using one on the other, eventually you will require both an new ring gear and new starter motor..
However bee careful, there are early verto clutches which have inertia ring gears
So best advised to stick with like for like... and the better of the two is the pre-engaged.
The lightened flywheel will not allow the engine to rev any higher than it wouls before, just the time in which it takes to get to that redline.
As for swapping flywheels from one A Series transverse engine to another.. yes you can... they are essentially the same engine
The ones you cant transfer the fly from are the inline Morris, MG's etc rwd cars, and the later autsin montego maestro engines which have a different gearbox and hence flywheel.