Does each of the size of the LF1/LFW/LFX manifold insulators allow to retain the engine cover for a VE Commodore?

Conservatively put, the 6.35mm manifold insulator is the only insulator which would allow you to be able to maintain your engine cover in your VE Commodore. If you were to install the 12mm item you would have to remove your engine cover, while the 25mm would also require this along with modifying the cowl/trim towards the back of the motor to provide sufficient clearance for the higher manifold.