Asking price aside - just a subjective personal observation on this interesting discussion...
It would be nice to know for sure the provenence of the frame in question of course but (quote) "If you believe her to be a Holdsworth, it is a smacking good deal; if you believe her to be a Bob Jackson, it is still a very smart price"...
Well, I was an amateur?road man (massed start) ion the UK during the era that this frame was apparently built, and for the record it looks identical - even down to the fastback arrangement; to a "Ken Ryall" I bought in the early '70s and which was almost certainly sourced from Holdsworth.
At that time Holdsworths were held in reasonably high regard by the 'peloton', mainly due to the professional team that was dominant in the UK then.
However, Bob Jackson, Ellis Briggs, Woodrup, Dave Russell, Mercian, Pat Hanlon etc., etc., basically anything that?could be regarded as bespoke (rightly or wrongly) was far more desirable to us... There was, I believe, a perception / bias?that any Holdsworth really wasn't bespoke because of the large number of low-mid range frames they also produced. This is a bias that I retain to this day I'm afraid!
So, long story short - if this frame finally was proven to be a Jackson - it would be hugely more attractive to me personally, and thus I'd be prepared to pay a higher price (if I were in the market).
Ian Briggs
Luton, Bedfordshire, UK.