replacing valve seals on a 318 procedure?

You can use compressed air with an adapter screwed into the spark plug hole to hold the valves in place. Then, you'll need the correct "head on block" valve spring removal tool. A small magnet is also helpful to get the retainer locks out.

If you have the "umbrella" style seals be careful to not cut them on the sharp edges of valve stem top. Most seal kits come with a small plastic tube that you fit over the valve stem top when installing the seal to prevent seal damage.

Hope this helps.