Well Im only guessing, but you pretty much have a stock powered engine assuming its assembled correctly. Take a little off for switching to carbs, then add a little for the carb/cam combo. You start out with about 135 whp so Im not sure which way or how far that way it will take you. That is where searching comes in handy, you can look at real setups and how they worked out.
Look in the L6 section FAQ. It shows all of the different heads and how they differ. I think your talking about the l28/e31 combo. Id reccomend searching and also getting "How to modify your L series" I know you mentioned early z engines but the p90 is pretty popular with flat tops.
My personal opinion is go turbo, your not limited as much as you are with a NA L series, but its up to you.