Your ultimate boost has mostly with C/R, twin-plugging and IC-efficiency (and combustion-chamber shape, and fuel octane etc. etc.
) to do.
With EFI, you can boost less and still get same power or boost the same and get more power.
First thing to ditch would be CIS, in my case. check out Tony's Megasqirt, it would work quite nice together with Carrera plenum.
So possible combo for you could be something like this:
Carrera crank, 8.5:1 trick rods and pistons, Carrera intake, Tony's Megasquirt, Carrera (or SC) single-plugged heads, hi-flo K27 and hot cams (as hotter than SC)...it would bring you to approx 400 hp w/o too much fuss and rev to high heavens with little lag.
There are people turbocharging their US Carreras which have little lower C/R than Euro models and it supposedly works fine with 0.5 to 0.7 boost.