Bob
Anthony Pearson at Classic and Vintage Bulbs (in Adelaide, Australia)
Home Page has a Q/H bulb for the prefocus base (the one in the PF770). This is a simple replacement.
I tried it, and it did make the lights very much brighter (much better than the previous dim glow). However, it did rather highlight the poor reflector design - the lights were more like flamethrower spotlights with rather poor spread/coverage.
I reverted to a modern 7 inch headlight that takes H4 bulbs - much, much better for driving, and can be set up with a nice pattern that doesn't dazzle other drivers.
regards
Julian