The 701 intake setup is vastly superior to the one on a 650 , they look similar but perform QUITE differently , as Kevbo said the cases have to be enlarged to clear the sleeves on a 701 cylinder , my advice look for a Waverunner lll with a 701 61X in it , pull the 701 out and put it in the Superjet , put the 650 back in the Waverunner and sell it , in that ski it basically runs no different , Waverunner lll's are cheap and at the start of the season pretty they are easy to sell and get rid of.
I did a swap for a customer almost just like this a few years back ,only difference is it was a Waverunner VXR pro donor ski SKI which has way more Superjet compatible parts on it, jet pumps , intake grates , ride plates, midshafts and housings all the same as a SN Superjet . The driveshaft is a different length though .