To my knowledge all the Ilmor bolt on stuff is the same, pulleys, belts, pumps etc.
I don't think you are going to be able to retro fit a Merc pump based on the mounting plate, location, pulley style etc. My engines have been outfitted w/ Hardin pumps which use the std merc impeller, gaskets, o-rings etc.
The KPM is a nicely designed pump, the ones sent to me were preproduction & didn't function properly. I don't believe they are distributed in the USA anymore.
Not sure when you expect to take delivery of your boat but have faith that Ilmor is working diligently on a drive solution. You should have both a Teague or IMCO drive option.