630rich, I've read all of the posts here and it looks like I am going to disagree with a lot of people. My opinions on this one will be based on some facts and some experience.
Fact #1: The displacement of a WC engine with 4.125 cylinders is increased from 201 to 214. That is more than half way to the WD-45 displacement of 226. If they maintained the compression ration of the original piston, it would suggest a 7% increase in horsepower - from about 28 to 30. Fact #2: Every 4 1/8 piston I've ever seen is a flat top which will provide a significant increase in compression ration. Theoretically, when compression ratio is increased, the power output increases by the same ratio. Since we don't know the after compression ratio, it is a guess as to how much horsepower will increase from the compression ratio change. Fact #4, M&W was one of (or maybe only) piston and sleeve maker in the 50's that pushed the larger cylinder. They advertised a 7 horsepower increase for the WD and the only difference that I am aware of between the WD motor and the WC motor was RPM. The difference between a WD and a WD-45 is about 8.3 HP. So the M&W cylinders almost get to the WD-45 horsepower. Since you've made an adjustment to rpm, you may have reached the rpm of the WD - RPM being the major engine difference between the WC and WD.
With all of the above facts, it seems quite likely that your horsepower has improved significantly. The starting hp was 29.93 on the belt. Changing displacement, rpm and compression, may have boosted you from 6 to 10 horsepower - put hp higher than the WD but perhaps a bit less than the WD-45.
When I was in high school, my family farmed with two 1939 WC tractors. I lived in southern Minnesota in black soil country. We pulled 2-16 plows in second gear accept in alfalfa when we sometimes had to go in first on old hay fields. We pulled a 10 foot tandem disk. When we had one of the WC's rebuilt with 4 1/8 cylinders, that tractor could pull the 2-16 plow in third gear (didn't do it except for test because it threw the dirt too far). The rebuilt tractor could pull the 10 foot disk in third gear easily - no strain in 3rd with either the disk or plow. Since the advertised speeds for 2nd and 3rd are 3.5 and 4.75 mph, that WC had an increased hp of 35% or about 10 hp. Remember, we had it rebuilt because it was tired so it probably didn't have 29 hp to start. We also bought a WD with 4 1/8 cylinders. That WC could keep up with the WD on all tasks - couldn't observe a difference. Later on, we rebuilt the other WC with exactly the same results.
Now for opinion. The original WC hp is listed as 29.33. Based on what you have said, I'd guess your hp to be between 37 and 40. You did all these - displacement, compression and rpm. Increase any of these and hp theoretically will increase proportionately. Increase them all, and the effect is additive.