alan, agree on the output buffer. however, if you use an input gain pot on a fuzzface type, this also seems to solve the problem. makes sense, and lets you have one less buffer in chain when your wah is on without the fuzz. besides, doesn't the fuzz go before the wah?
i also agree on the 100K/33k voice resistor. it depends on a bunch of the other stuff in the circuit, it is possible that this mod works well with mostly stock gcbs, not sure. anyway, tune to taste once other components have been changed if youask me. plus, some people like the wah tone of the early vox or colorsounds that had no resistor at all in this position.
as far as the input buffer of a gcb, in my testing, for the wah tone it adds a little balls and some extra high end vs bypassing it, but again, if you are going to mod the whole wah, this difference becomes fairly minute. leave it in if you want a modern wah with strong treble, take it out if you want a vintage warm old time sounding wah , in general.