Dave at Puma Race Engines fits 45mm intake valves. His opinion is that the evhaust valves are plenty big enough. He also fits different guides and seals as you can see in the pics of my head above. Bigger than 45mm is not going to fit and be safe.

For a european CVH to really rev, the valvetrain needs sorting out. There used to be roller rocker kits on the market, and if there is enought interest they might be persuaded to do another run.

Solid lifter cam kits are available, from Mike at Ferriday Engineering for example.