Terran C's method is the best way to do it, because you can specify components for as many sizes of vehicles as you want, not just 2 types like with fake engines. I need to update the mounts section of the tutorial.
Ah, thanks for the workarounds guys, the mount system will be perfect, seeing as you can attach both minimum and maximum ship sizes to mount types, and of course tech requirements so I can make custom mount sets for each racial tech paradigm.