I wouldn't even try the conversion.
I won't waste your time telling the story of trying to get Olympic Arms to make HP conversion barrels. Their prototype never worked right.

The Pachmayr grips for the HP originally designed for the Practical solved the problems for my hands. They are far superior to the wood grips for control and comfort. I sometimes shoot a HP .40 with major loads in USPSA/L10.

If you want to go to a lighter recoil spring, you can handload to .40 minor, which is an even lighter kick than commercial 9mm.

If all else fails, trade it.