For the cost of adding any kind of boost, either turbo or mechanical supercharging, you can do a lot of more conventional go-fast modifications. You'll need to do an engine rebuild in the process, however. The 250 has dish-top pistons that serve to lower the compression ratio to emission-controlled levels. By substituting flat-topped 307 V-8 pistons, which are a direct replacement, you'll get a compression boost. I've built 250's with pretty radical cylinder head milling, .050" in one instance, without piston-to-valve interference problems, but I was using a stock cam in that one. If you can get away with a fairly radical grind cam AND high compression, that's the best of all possible worlds, because the compression bump compensates for the reduced cylinder volume created by the longer duration cam on the compression stroke. In most cases, the effective cylinder pressure isn't much more than stock, even with high-compression modifications. Using a radical cam WITHOUT increasing compression is a huge mistake! Improve the intake and exhaust with appropriate manifolds, and add a high-performance ignition system. You'll spend about as much as adding a turbo or a blower, but the power increase will be a lot more noticeable.
Jerry
