Can be done - my coupe with L20 had 158Hp at wheels on a conservative dyno.
Step 1 - buy my cylinder head from this motor. 78 deg cam, Datrats adjustable gear, big valves, ported and set up by Cave Hill in Melb - even Errol is impressed with it!
Step 2 - BIG bore, flat top pistons (teflon coated skirts etc)light flywheel etc.
Step 3 - buy my old 45 webers from the guy in QLD selling them on Ozdat. They are mached out and set up for the above head!
Step 4 - have plenty of cash!
It can be done but beware outrageous claims - my 150 Hp engine could pass blokes who said they had 175 - it's all about the torque really ....
Cheers.