Is this an A12 engine? The A14 head is better for street driving than a GX head as it has smaller ports (but still much bigger than A12 head). This is a nice upgrade for A12 if you keep the engine for 4000-6000 RPM operation (for under 4000 RPM, the A12 head is better). You will need A14 oval-port head, intake & exhaust manifold + exhaust pipe stub (3-bolt pipe for A14, 2-bolt for A12).

When fitting A14 head to 1971-1973 A12 engine, drill/grind the oil passage in the head.

Note that there are round-port A14 head which will work too, about the same as A12 heads.