When in the motor trade, I used a compressor connected to a heavy duty flexipipe which was in turn connected to a threaded insert mated to the other end of the pipe which fitted in the plug hole.
The compressor was set to 100 psi and allowed to build up pressure in the cylinder, with the rocker box off it was possible to use a socket that covered the valve spring top and short extension bar to ‘Shock’ the valve spring top with a plastic faced hammer to effectively make the two collets fall out.
The socket contains the collets stopping them dropping into the head, you’ll know success as you’ll feel the springs pressure on the socket.
Replace valve stem oil seals using thin plastic wrap on the collet indents to prevent ‘cutting’ the new seals.
Replacing the springs was effected by using a 2inch long tube that was slightly bigger than the valve spring top, this had a small recess into it preventing the top moving out under pressure,, the tube had cut outs big enough to use a screwdriver coated with grease to relocate the collets.
The tube was welded to a foot long round steel bar that had a 4” wide ‘T’ piece that chest and body pressure was enough to compress the springs down to insert the collets, once both valves are done short rap with plastic mallet to ‘seat’ the collets.
Explaining this seems long winded but shorter than removing the cylinder head and possibly the barrels to replace the base gasket as well as the head, it worked for me on over 50 applications
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