Id bet $ u cant swap the aveo heads, and yes the vvt aveo is a completely different program. The 1.6 vvt aveo and the 1.8 aveo share 90% of parts including the ecu. I think the plastic manifold will hold reasonably well. The 1.4T guys also have a plastic manifold and it seems to hold near 20psi just fine ( if I read correctly ). To boost an aveo vvt to 8-10 psi would be an accomplishment. u can check the Sonic forum to see the 1.8 guys ideas. It sounds like u want to revert to the Daewoo based E tec II, I wouldn't, but to each his own. The vvt motor already has a iron block and parts can be found from opel/vauxhal engines to build a bullet proof bottom end. Good luck...