915 valve question

I see you trapping around 6100-6200 depending on the slippage. I'd make it higher than 10:1 by whatever means you have to use. Milling's fine so long as it's done right and there's the understanding that things like pushrods will need to be replaced and the intake and heads will be a permanent package. I think the M1 would work if you have it, but I think the RPM would be a better power producer. Not by much, but more torque and with only 3K stall you still need torque. If you can get a race convertor up around 45-4200 that would help. As for a cam, I'd use the XS274S, and get a set of 1.6 rockers for it.