hi ralf, i have to say, looking at GAD's pics the head size of his looks slightly bigger and closer to original than mine but that may just be the angle but see what you think when mine get to you? as GAD mentions, with 3 on a pickup you'd never even notice as they look pretty close, it's only side by side (and if you're looking closely) that you can notice much difference.....but there is a difference! i was just thrilled to actually figure out the right thread, pitch and length that worked so i could reinstall some HB-1s on my S100 again.
the ones i have for sale are definitely slightly smaller but that's all the company could supply when i asked about head size. i guessed it was because they just start with a blank and thread it up as required and that the modern blank is slightly smaller - maybe even metric- compared to the original Guild ones? BTW, obvious question maybe but when did they actually stop using this size and style of screw and are modern Guild ones different (i assume they must be)?
i've attached a pic of one i put on my M-85 bass to show them side by side and another to show six on a surround. the original screws look chrome plated to me as you mention and these are just stainless steel so that's another difference (but at least they should stay shiny!!!).
one last thing, if you can actually source a "perfect replica" i'd be up for buying a few, though i'm happy with the ones i found so far.