L20ET is already compressing at 7.5 - how much lower do you think it needs to go?
Couple of things I know about the engine:
a RB20 / RB25 turbo bolts straight on, so there is potential to get something extra out of the engine.
It will probably tolerate some extra C/R, so fitting flat-top pistons may be possible.
Std) L24E has tiny ports in the head. And a tiny combustion chamber. It might go better with a 240Z head (larger ports, larger chamber - is that the N47?), and 240Z flat-top pistons.
L28ET is probably the way to go.
If you want forgies for the L20 (or any other engine), talk to Bill at Australian Precision Engine Parts in Melbourne (03-98871299)
Hope that helps some.