Front head shouldn't be a problem, might need to remove the radiator; it's the rear that might be a bit messy. I'd almost drop the engine though. It doesn't take that long beyond what's necessary to get to the heads.
"All that is gold does not glitter,
Not all those who wander are lost;
The old that is strong does not wither,
Deep roots are not reached by the frost."
'12 690 Enduro
// 690 Wiki