I run a TSR pack D head which is ported and polished and has larger valves (40.5mm inlet with 7mm stems and large cutback, 35mm exhaust with heavy cut back). This is run with a TSR 202 cam, three angle valve seats also. Sit that on a 2l bottom end and it goes alright. Got 35mpg out of a tank yesterday also. I have mine set up for point to point rather than top end so my cam comes in around 3500rpm but I could really do with a wilder cam considering the head work. A vernier pulley will allow the power band to be moved around and honed in if you do get a cam.