Sorry Im kinda confused here. I see you want to change your valve stem seals (lol). Im going to assume you know they are bad for sure. I also see that you've posted a thread looking for a new 420A head. What would be the point of buying a new head for just the (used) valve stem seals? And if you are willing to take the head off to swap, why not just change the seals on your existing head? This way you could swap your cams and sell them as well (not sure why you'd wanna do that either tho).

I was able to take apart a 4g63 head and replace the valve seals, lap the valves, and reassemble it in about 2 hours. With no special tools, no prior experience. All you need is a big ass c-clamp ($8 at Harbor Freight) and a spark plug socket for removing and reinstalling the retainers. Cost was about $50. 8 for the clamp, 32 for seals, and about 8 bucks or so for the valve lapping tool and compound.

Whats the problem anyway? Is the motor just smoking a bit at idle? Or are you leaking air on boost leak tests/leakdown tests? Losing compression because of it?

just curious lol