The retainer kit we are using (TFS-2500286P) has shorter valve seals than stock to clear the additional compression of the spring from the additional lobe lift of the cam.

Proform's new Pneumatic Valve Spring Compressor can cut cylinder head disassembly time in half. Pulling the tool's trigger supplies up to 350 pounds of force using 125-psi air-compressor pressure ...

It's a good idea to lightly tap the retainers with a soft mallet to loosen the valve locks and then bolt the spring compressor tool in place over the pair of valves.