The biggest gains are going to be in the bowl area and with the installation of larger valves. I would focus on the areas that will yield the biggest gains and then go from there. Also, keep one thing in mind, that regardless of what you do to increase the power and performance, its still a flathead, and your only going to get so much out of it, so I would only focus on the tried and true methods for getting any gains. The cylinder head swap is a plus, its also the first step for those building the Straight 8 Pontiac's. Relieving the block is also beneficial, so I would add that to your "to do" list along with the porting and larger valves. You might also look at a turbo or supercharging it with an M90 centrifugal supercharger, it will add a bunch of power for little money.
