Hi Daniel,
The photos below show the Solent stay at the bow and the tensioning method at the mast.
The stay (blue Dyneema) is about 400mm back from the forestay. It runs through a spare genoa halyard sheave at the masthead and back down inside the mast. It is tensioned at the base of the mast by 3mm grey Dyneema running through low friction rings, ratio 6:1.
The Solent stay and forestay get closer together as they get nearer the masthead. The sails on the Solent stay stop well short of the masthead. Therefore I don't think the stays getting closer will be a problem.
I will probably attach the Solent stay to the front of the mast in the conventional manner next time I take the mast down. I will then tension it with a Highfield lever at the bow. Attaching it to the front of the mast will halve the length of the Dyneema (reducing stretch) and take the force off the masthead sheave. I think the existing sheave is metal as it was installed for a wire halyard so should be all right in the short term.
I can use my old genoa halyard to raise the sail on the Solent stay as the roller furler on the forestay has an integral sheave at the top and its halyard returns back down to the drum.
Steve