Its going to be a bitch to do w/ the head on the block... I can tell you that.
Shit, its a pain to do with the head off the block
Why are you so certain the rings arent bad?
Anyway, to replace the valve seals...
You need to:
rent/buy a valve springs compressor
get a chuck or adapter for an air hose to be screwed into your spark plug socket. this is to prevent your valves from dropping when you remove the retainers/springs... etc.
1. turn crank so #1 and #4 are at TDC.
2. remove valve cover and distributor
3. remove cam cap bolts, cam caps, cams and rocker arms.
Here's the valve spring compressor part number from snap-on YA8845 w/YA8845-2A 7/8" attachment
4. tap valves with rubber/plastic mallet to loosen the keepers.
5. install spring compressor, compress springs and remove keepers
6. you will need a valve guide seal remover to remove nad to install the new seals.
7. intake valve seals have a white spring, exhuast have a black. you'll notice the difference.
8. assembly is the reverse of disassembly.
Good luck.