I'd like to redo the valve seals on the motor I'm swapping into my trooper, but I don't want to pull apart the head since the gasket is in good shape right now. Has anyone done this, and are there any tricks.

Seems to me that I should be able to pull the valve springs and change out the seals without losing a valve down the tube so long as I do each set of valves with their piston at TDC. I've also heard of pumping compressed air into each cylinder while the valve springs are off to hold the valves in place. I'm not sure I'd trust that alone, but the valves can't go far with the piston at TDC.

So, anyone have any input on doing this? I'm trying to get this motor as fresh as possible without cracking it open too far. I'm already swapping oil pans, replacing both crank seals, basically all the external gaskets, so if I could hit the valve seals too that would be as close to a rebuild as I could get without pulling the head. Any tips, ideas, or discussion?