I installed a RKT head this year, I had to measure the distance from the top of the piston to the top of the jugs. I do not know what sled your running, but for my 2000 Doo 700 there are 3 base gaskets to choose from. I would try and talk to Kelsey before you purchase the heads.
If you go on snowest.com, look for RKT(Kelsey). He will answer any of your questions. you can also check out their site 2strokeheads.com. Kelsey has alot of good info on there.
2003 Yamaha RX1
1997 MXZ 670
1995 XCR 600