226/201 engine build

I'm not exactly sure what you are seeking here, and not sure there is an exact answer due to soooo many variables.  A model WD gas was a 201 and was rated at 34 PTO HP @ 1400 rpm. A WD-45 gas had the same 4 inch bore and a 4 1/2" stroke which gave it 25 more cubic inches. It was rated at 45 PTO hp. BUT, it wasn't all about 25 additional cubic inches. The compression was raised from 5.5 to 1 to 6.5 to 1. The carburetor and air cleaner were larger. The intake/exhaust manifold was better flowing. So, it took 3 changes to gain about 10 HP. Let's look at the WD-45 and the D-17 gas engines. Both engines were 226 cubes. The WD-45 compression was 6.5 to 1. The D-17 was 7.25 to 1 with the same 4 inch bore. The carb was identical between the two tractors. The engine speed went from 1400 rpm full load to 1650 full load speed. So, the D-17 engine got more compression and an increase in speed.  The model 175 gas tractor was still 226 cubes had 8.25 to 1 compression, and higher lift camshaft, a slightly larger carburetor and rated speed was now 1800 RPM instead of 1650. It gained 10 more flywheel HP over the D-17 engine.   Now, what is your question ??   You can have more cubes with lower compression and have LESS HP. Carb size affects HP output, as does engine speed.

More cubes, provided you keep the compression high (say 12 to 1 or greater) makes more HP.  So, just boring to 4.630" with your current 4.5 stroke is only 302 cubes.   Staying with your current bore of 4.125" and stroking to 6 inches yields 320 cubes.  So, doing only one thing will improve HP over what you've currently got, but you will fall short of 100 HP for sure. Doing both 4.630" bore and 6 inch stroke will get you to 400 cubes. That old myth of longer rods make more HP isn't really true. I have beaten many "big" A-C engines with longer than stock rods over the years with my shorter than stock rods. I have had stock valves and BBChevy valves (two different engines with same B & S/cubes) and seen little to no improvement on an 1800 RPM engine. I believe the key is making sure your compression remains high, like 300 - 320 psi cranking compression. And setting the ignition timing to the optimum BTDC number to make the most torque/HP. My engines always require 110 fuel minimum and 114 is better.  Something to think about:  a stock G-226 in a model 175 tractor makes 70-72 flywheel HP @ 1800 RPM. Using that info, if you keep the same HP per cubic inches ratio, 400 cubes should be 124 flywheel HP @ 1800 RPM.  A mighty One-Ninety XT with 301 gas cubes produced 100 flywheel HP but at 2,200 RPM. If you slowed it down to 1800  RPM it was only barely 90 flywheel HP.  If you made it 400 cubes with the same HP/cube ratio it comes in at 120 HP. A larger carburetor venturi and CFM (in my mind) very well makes more ooomph than big valves on an Allis engine at 1800 RPM. Now, at 3000 RPM that is a different story on the big valves.