novak motors are 36mm diameter i think, (basically 540 size), they say it will only fit their motors because they want more buisness
the HV max motors can probably only handle 1000w max, a medusa 80mm motor is 36mm diameter but would be overkill for a buggy, a 70mm will still pull strong
http://www.rc-monster.com/brushlessmotors.php?pg=3 this has all the specs for all the medusa motors
here's a brushless mount for the hyper http://www.rc-monster.com/proddetail.php?prod=rcmhypermount