[Bobboloo]

There are others way more qualified to offer suggestions but I would think the particular circuits you race on would be the real determining factor for you. Each one being unique and having it's own requirements what is the best compromise for you?

Is it in your best interests to trade off your present torque curve for one that moves up the RPM band for bigger HP numbers?

Could your needs be better served with tranny gearing?

Considering that being a period race car is your limiting factor I would look to Porsches past experience in the matter inre. valve and port size.

We know that they went to the larger valves (I49 E41.5) with the 2.8RSR which used 43mm ports. Before this the largest port size was 41mm with your present (I46 E40) valve sizes. So I think it's safe to assume they felt 41mm was the largest port that the (I46 E40) valves could efficiently support.

41mm is a substantial increase to your present 36mm ports so it seems there is plenty of room for peak HP increase with your present valves. This is good considering the cost of RSR heads. We know per BAs book that Porsche made at least two race motors with the 41mm ports. 911/70 a longstroke 2.492 liter which made 270hp@8000 and 911/73 a shortstroke 2.464 liter which made 275hp@8000. Both motors used 906 cams, I46 E40 valves and 41mm in. and ex. ports. So realistically you could build yourself a 2.7 liter 906 race motor probably good for atleast 285HP with your current I46 E40 heads.