Go with an 8000 RPM cam and springs, easily make 100 rwhp. This will need ported H89 head. If you fit larger valves maybe 120 rwhp? For 100 rear-wheel HP, go with Weber 40s and start the jetting with 32mm chokes.

The H89 head with port matching makes maximum HP at what, 6000-6400 RPM? Rev it any higher and it goes slower -- regardless of the cam. So with this head and if you like to rev to the limit, recommend a GX-spec cam but doubt if it will return 100rwhp