you don't need to take the head off to do stem seals as long as you can compress the valve springs and remove them with the head on.

you can do this by pressurising the cylinder with air and having both sets of valves closed if you have the right tool i made one by cutting up and old spark plug and brazing on a length of steel pipe and then a brass fitting on the end that i can connect to an airline.

you may also be able to do it by removing the cam belt, and moving that piston up to tdc so that when you press on the valve spring, the valve contacts the piston and can't move. i wouldn't advise it though, cos to remove the collets you normally have to give the springs a whack with a hammer to release them