Four years ago when I purchased a Toro 726 2-cycle (now called the 6000) it was advertised as a 7 hp engine. I suspect that does not mean the same 7 hp in a single-stage machine, but I would expect that it is either the same hp as the 421 or better. Given the nearly identical specs + the fact that I don't mind mixing the oil/gas, I'd prefer to save a BenF...but that's just me.

I'd think 7 h.p. is seven horse-power, no matter what it is in, or on. Engine design, especially what you can see without tear-down, doesn't necessarily show how much H.P. it puts out.
Heck, those very old, antique engines, single cylinder, ran on well-head gas, weren't of very high horse-power! Big, but not powerful, lots of torque, not much H.P.!
Horse-power is a rating! Why it hasn't been changed to a more usable term escapes me. But, we've been brought up on H.P. Its easy to figure out!