I made a little fixture and it worked for me. The fixture is a piece of 1/8 inch plywood, drilled some holes to match the head bolts. Glue a piece on the top of the fixture roughly the shape of the combustion chamber in the head. Bolted on the fixture. This allows one to put down pressure on the valve springs with the valves not moving down. The keepers are easily removed at that point. They are tiny but work the same way as big old gasoline engine.

Once the spring keepers are removed, the springs can be swapped out. It is a tedious process to get the spring keepers reinstalled but a wife watching over you helps. Prevents certain curse words and adds a set of eyes to spot an errant keeper flying off somewhere or other. Take your time.

Cheers,

Chip