Six of one, or half a dozen of the other?

If the existing 170 is in good shape, add your performance parts to it and run with it. You can always start with a spare 225 (people give them away) and swap it all over later. The 170 has the advantage of a smaller stroke, which gives it a little less displacement, but it makes it a better engine in terms of RPM. When a stock 225 is running out of breath at 4000-4500 RPM the 170 will wind higher, plus the modifications you intend to make, presuming Intake, Headers, and ?