SuPer SiX Slant Signet!

Usually, there is a direct relationship between power and mileage.....as in, more power, less mileage. Some items can be replaced to give more in both cases (like creative cam grinds and fuel systems) but in general, you'll have to decide which you want more. How about taking the pan off the 225 and see what it needs? If the engine didn't smoke, has good compression, and looks decent inside, you might be able to get away with a crank kit. That shouldn't cost too much....maybe a couple hundered at most....not counting your labor!