I would "GUESS" with no other mods, adding a small four barrel on top of say the Offy intake and some Clifford headers would probably get you from the factory 14HP rating to about 175. MAYBE. Certainly by including the head milling on top of all that. The problem is, the 225 never got its own cylinder head. It has to breath through a head designed solely for the 170. Chrysler never redesigned the head for the 225, so that's "all we got" unless you install bigger valves and or port. They respond very well to forced induction, but then, cylinder head mods are nowhere near as important, as you're pushing the mixture through the engine, instead of relying on a low pressure era at the mouth of a carburetor. That is a much different story than forced induction and needs "all the help" it can get.
What I would recommend would be this, if you don't want MAJOR mods. Find a factory super six (two barrel) intake and carburetor. I would use a Carter BBD off a 318. MUCH less expensive and MUCH easier to find. Like an early 70s version. hog out the outlet to a stock manifold like I had my friend Freddie do here:
Exhaust Manifold Mod
BUT the important thing here is USE a 2.2 or 2.5" pipe, NOT the stock 1.75 pipe, or all that work in the manifold is for naught. And use the bigger exhaust ALL the way back with a good, free flowing muffler. You'll also want to give the distributor a good performance advance curve. Those mods all together will make a nice increase in power AND mileage. Then you can decide later if you want to do head milling, bigger valves, porting more camshaft and such.
