Found some Viton stem seals today at the local cylinder head re-manufacturer for 20 bucks. These ones fit snugly over the guide so I decided to go with them.
To get the valve springs off I made a fitting for the lower plug hole and pumped compressed air into the cylinder with the piston at the bottom of its travel and both valves closed. This held the valve up nicely while I removed the springs and collets with a modified spring compressor tool thats used on cars. It all worked a treat and took less than 15 minutes per cylinder to do.
Now to see if my $20 investment makes any difference to the oil consumption or not
Cheers
Graham