From everything that I've read and seen, the head needs to machined to fit the Hot Cam on the exhaust side. It's not one of those huge things, but the decompressor is too thick.
Here is the info. Any machine shop should be able to handle this. Shoot you could probably do it at home with a grinder and some patience.
http://www.dirtbikeworld.net/forum/s...ghlight=hotcam