gday mate
this is my limited knowing of flywheels

the a14 and a15 flywheels are thicker then the a12
the a12 flywheel is lighter

if the bolt spacing is the same as a15 and a12 flywheel it should fit straight up ( im unsure about this )
but there is stories of guys using a14/15 engine with a12 flywheel due to its lighter weight so id say its the same

as for the gearbox if your using the a12 F.W and standard 4 speed then you would use all the standard gear, (clutch, pessure placte, thrust bearing etc)..
the starter motor mounts to the gearbox so using your a12 starter should also not cause any problems

before putting it all together make sure the a15 you get has a spigot bush,, if its out of an auto car it wouldnt have one

so if someone can answer the question.. is the flywheel bolt spacing for a12, a14 and a15 all the same?

hope you can make some sense of all this
cheers
Jason

edit: some of the questions were answered while i was writing my reply

Mildman is correct!

I believe they are interchangeable, the A12 one is lighter than the A15 too.

Hi All, Ive read the wiki but not sure if there is a prob here. Hopefully getting an a15 this weekend to fit into my B110 sedan, I have a ute crossmember and have changed the wiring for the altinater, there is no exorst fitted in the car and will run a freeflow so not a prob with the height differance. But is there a prob with the flywheel? the engine im looking at buying has,nt got a flywheel and I will use a standard 4 speed just to get the car going.
I guess my questions are,

Is there any diff with the flywheel from a12 to a15, if so witch one do I use? if there is a diff will this create a prob with the starter motor? and do I have to fit an a12 flywheel to fit a 4 speed? Hope this is enough info

Thanks in advance......