Yeah in all seriousness do your best to find a 1400 block. Im not saying anything is wrong with the 1200 but by the sounds of it you want a quick car for as cheap as possible. The bigger engine is the way to go. It is a much better starting point.
Wrap up the 1200gx and keep her stock. She will be worth more that way plus you will feel better knowing you didn't ruin one. Maybe use the head on the a14 but definately use the manifold and hitachi su's.