The stator is rated for about 180 to 190 watts at high RPM's, so as long as you don't have a high output headlight bulb you should be good. Just add up the watts. I wouldn't go for the full number as you are not always revving to the max. Maybe go for 150 watts.
- Headlight 65 watts on high beam. Leaves 85 watts
- Tail light 10 watts (?) leaves 75 watts
- Ignition 20 watts (?) leaves 55 watts
- battery charging reserve 20 watts leaves 35 watts
I'm pretty sure that is overly conservative, so I'm sure that the heaters will be fine. Now if they are 35 watts each then it could be a problem.