Honda sells generators that were specifically made to run on NG. I have seen many, many standby generators from your size all the way up to a 65kw system that were built to run on NG. That part can't be illegal. And if it were illegal to convert one to NG, would fleaBay allow so many sellers to offer NG conversion kits?

If you can replace a carburetor, you can install a conversion kit. If your plumber is willing to hook it up, then why not? If you are going to run it through your breaker box, I would suggest having an electrician install the proper switch gear.

ETA: Your outputs may be slightly changed, lower, running on NG. It has less BTU, so it produces less power. I wouldn't think you'd lose more than 10-15%.

__________________
Insert short witty words here