I had a RC585 with a single 175 2 stroke on the back, I now have a RC6.4 with twin 115 etecs (2 strokes). The 6.4 with the twins is heavy on the back end & you need to balance the boat to get the best out of it. I have twin batteries up front in the console & twin fuel tanks. If the boat you're looking at was originally fitted for a single, chances are it will have the cutaway transom & could be problematic fitting twins. My 585 used to take a fair amount of water over the stern when we had divers onboard. Twins would be worse, the 175 engine was the same block as the 135/150, so the same weight.
Personally I'd stick to the single 150/175, check the rating plate, they DO vary.
PS, the 585 with the 175 2s was FUN!!!
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5