A stock Z1 head only flows about 70 CFM (intake side) with a .500" lift cam, but a pro ported big valve Z1 head will flow +110 CFM depending on how big you push the runners. Since all engines are air pumps the more air you can push thru the more potential HP it will produce.
You want the head flow to at least match what the carbs can draw thru. Your RS34 carbs flow about 114 CFM (per Larry Cavanaugh) so you can open up the ports on that head a lot more.
Once you big valve the head you deck it to bring the compression back up lost by sinking and de-shrouding the valves. This is where you can also boost the cranking compression to over 200 PSI. You also want to run higher lift cams (+.435") to take advantage of the increased air flow. All of this requires mocking up with clay to make sure everything works together and has proper clearance.
Injected is spot on here. Although, as the old saying goes, "speed is money, how fast do you want to go?". I'd say that if you're going to go all in on a cylinder head/piston combo, please make sure that the bottom end of the motor and trans are up to the task. If you're tempted to take a shortcut anywhere in the process, ultimately it will come back to bite you in the a$$.
And, to address Southpaw's original question, I'd say that a shift light is a whole lot easier to see after launching and while making your way down track. Although, without a datalogger of some sort, you'd still need a tach to see RPMs when going through the traps. If you can integrate a shift light into your setup, life will be a bit easier and your runs will be more consistent, IMHO.
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