OK, the hp for a WC according to Nebraska Tractor Tests:
1934, test 223 - 21.48 hp on distillate
1938, test 303 - 25.45 hp on distillate
1938, test 304 - 29.93 hp on gasoline
No idea what the difference was between test 223 and 303, since my book doesn't show compression ratios. All of these had a 201 cubic inch engine. Note that the gasoline tractor has a higher compression ratio than a distillate tractor, so burning gasoline in a distillate tractor will work but won't give you that 29.93 hp.