The engine thing is a dilema
I have the engines I am considering
BMW (980): Reasonably cheap to buy, good supply of secondhand bits

quite expensive to tune to be competetive. Reliable when tuned by the right people. 110 bhp at crank 18% loses in drive train.
Trident (bored to 930): Very expensive to buy and tune

Heavy

sit in chassis well

sound wonderful

Again reliable when tuned by the right people. Approx 100 bhp at crank 12% loses in drive train.
Honda CB 750 (bored to 830): Cheap to buy

cheap to tune

Very heavy, big lump

tubes have to go over engine / carbs

Dry sumped standard

Power to weight ?? 67 bhp at crank std 750 12% losses in drive train.