I just want to say Thank You to all that gave their advice. One other thought what would happen if I used my 73 340 heads ? Should I shave them or leave stock?
What you intend to do and where you want the peak torque, rpm to run it at.
You could experiment with 1.88 and the 920 heads.. or... what are the 73 340 heads you have...1.88 ? Drop 11/32 1.94/1.6 intake/exh valves in them. As for the 920 heads... If you are able to get the low/mid lift strong and typical 360 head flow peaks ...that would be neat