The P90 head was introduced as the "turbo" head in the USA and other markets which had the 280ZX turbo models. The "flat top" pistons were used in the normally aspirated models to restore a reasonable compression ratio.
Thus the poor man's turbo engine would consist of the P90 head on an early dished piston block (79-81 with N42 head). The ideal would be to build it fresh using new turbo pistons (although these are hard to find in oversizes). This will provide a compression ratio of about 7.4:1 or 7.5:1 with a 1mm overbore.
Useful additions would be extra fuelling, either from Janspeed style extra injectors or via fully programmable unit with bigger injectors. Some form of electronic ignition retard under boost would be handy....
