WhisperFlo motor up-sizing

[ColdPlungeGuy]

Greetings,

New on the board. Here's my question:

Am looking to upsize my WhisperFlo 2 hp, 2-speed motor to 3 hp, 2-speed. I have ID'd the Pentair 353316S as a candidate, but it is shown in the Pentair catalog as used on the WhisperFloXF. Picture looks like a standard 56 square flange motor, so I'm thinking it should work fine on my old WhisperFlo (assuming upgrading the impeller to 3 hp as well).

However, when I called Pentair, I got the standard disclaimer that "we can't recommend using that motor on a smaller pump". OTOH, the same catalog shows that my WhisperFlo was, in fact, offered with a 3 hp motor (just not 2-speed).

So, is there any known reason I use that motor on my WhisperFlo (not the WhisperFloXF) along with a 3 hp impeller?

Backstory:

I have a heatpump at a somewhat remote location with long plumbing runs. When I engage that loop, my flow decreases, not surprisingly. It's just enough of a drop such that the heatpump intermittently thinks the flow is too low. The easiest fix would seem to boost the motor hp, though I may have to look into a booster pump.