Cylinder head still on the engine, you need a length of rope and a manual transmission. Rotate the crankshaft so the cylinder in question has the piston down, add rope, leaving a tail, through the spark plug hole, and rotate the engine back close to TDC on that piston.
Engage 4th gear, and the engine will stay still while you mess with the seals.
A fitting is available to perform the same function using air pressure to hold the valves closed.
Wear gloves, and if you didn't get it the first time, wear glovs. The edges of everything on the top of the head will cut normal peoples' skin as they are not rounded at all. Wear gloves.
With the head off, you can 'jury rig' a Chevy style valve spring compressor to release the keepers. Set the head on a bench with a chunk of wood under the valve you want to release. Use the tool to compress the spring, and thump it gently with a plastic hammer or mallet to release the keepers. Remove them, and release the compression. Exchange seals, etc. You might take a look at the seats to determine if they need to be cleaned up using compound. Should be crater free and show a clean sealing line.
You can mark the front pulley with chalk to note which pistons are where. 1&4 cycle together as do 2&3. If the chalk is at TDC (noon) then 1&4 are at top. Move the chalk to 6PM and 2&3 will both be at TDC.
tom