Machine shop with the head, inspect valves, new seals, etc. as you almost certainly would. If head is good (likely) go for it and do all the little stuff needed while the head is off and you can poke around the engine at will.

Related question. Might need to do a headgasket on my 850 in the near future... what is the most likely cause of it leaking oil? I know that the prev. owner did that job and I am afraid that he might have installed some damage along the way, from other repairs I have fixed.. Issue is that it is leak...