piston rings

Something maybe 5/16" or 3/8" and flexible (floppy) that can be fed into the spark plug hole easily. Lower the piston, feed in some rope into the plug hole and bring the piston back up in the cylinder by hand 'til the rope pushes up against the valves. This is to hold them closed and keep them from dropping into the cylinders when you remove the valve springs and retainers.

This is all after removing the rocker shaft. Do this by unscrewing the 7 bolts 1/4 to 1/2 turn at a time in order to allow the spring pressures to release evenly. When you re-install after changing the valve seals, do the same thing: turn each bolt down a bit at a time to draw the rocker shaft down evenly.

Once the shaft is off, remove the rockers, bolts and separator rings and lay them out IN ORDER and keep them in order. Keep the bolts in order in the shaft; the long one has to go in the back hole.

If you use the old lever style compressor, then put the shaft back in place without rockers and separator rings, and snug the bolts down; this will be your leverage point to use the compressor tool to compress the springs one at a time. Stuff paper towel down in each hole where the pushrods come up so you don't drop a keeper down there.

Sometimes the keepers in the retainers will stick; I use a deep socket and gently smack the retainer with the inverted socket and hammer. Needle nose pliers will be good to pull the keepers out.