Don't know about the 42mm carb
. Mines a stock 40. I bought a used pro-r hyperchager without the mounting bracket and tried to fab my own mounts out of aluminum stock. I got it to mount but wasn't really happy with the set up. It required 40 and 50 mm
bolts to the jug and I thought because of the bolt length the stress on the jugs might strip the boss threads out due to vibration. So I ordered the mounting kit from Kuryakin...$120 CDA. Part #909420. You have to order direct from them through the tech. support dept..
I couldn't find a dealer that listed the part out of the kit,and even the Kuyakyn customer service didn't show the part listed out of the kit. The rubber transition to the carb has a dog leg in it. From the low the filter housing to the high, the carb throat is about 2" difference. The "Z" and "L" brackets distribute the mounting stress uniformly and keep the rubber in the right position. Kink the rubber and you'll mess up the air flow. There's not much holding the carb in place and the hypers are pretty hefty so you really need to have the right mounting assembly or your going to create air leaks around the mainforld. These things look great IMO but are a bit of a PIA.
We spec'd my wifes' 750 Honda Aero from the dealer with one on it and in three years it's never been an issue...rain or shine. I think it all comes down to maintenance and proper set-up.
One other thing, they do sit further out than stock. I removed the two 10 mm mounting bolts from the right floor board (underneath) and rear brake assembly and replaced them with 30mm and made a couple of 1 inch aluminum spacers to mount between the floor booards and the frame. This just brings the brake pedal out an inch so you don't feel like your bending your knee around the hypercharger. Works fine, anyway good luck.