Certainly looking like Mistral. Elan only had 531 main tubes and Special had less rake on the forks, I think. ca. 1980-81? Still has over the bb cable routing, but does have brazed cable guides on the top tube. Frame number on the bb shell should pin down the year.
Nick
Does your Elan have the wrapover seatstays like this one? And is the 531 sticker the same, of just a "main tubes" one? I thought not for the Elan, which is why I sided on Mistral, but I'm quite possibly wrong on that.
Nick
My 1950 Holdsworth is 12868, are you sure you haven't missed out a number somewhere?
"Road King" has a couple of Holdsworth bikes dated around late 70s / early 80s, maybe he can help with the numbers from his. There was a similar thread a little while ago, (with a fellow forum member trying to date a suspected late 70s / early 80s Holdsworth) he may have added his frame numbers to that thread to help there?