Hi, Neil & CR ---
I'm very curious about your possible Granby, but have no knowledge of their serial number sequences, so am responding only to the Hercules Kestrel portion of your message.
The Kestrel was a well-thought-of, quite popular and decent machine offered primarily to the club market. I've seen many, many ads for it in my old Cycling and especially CTC Gazette magazines from the early '50s. I can't access my mags at the moment, so can't tell you all the specifications, but I believe it was built with 531 throughout.
It's NOT a botique frame (Ephgrave, Hobbs, Hetchins) by any means, but a nice factory-built consumer-level rig. Therefore, I would offer only a moderate price for it (certainly $100 GBP or LESS, depending upon condition, of course) unless you have sentimental reasons for wanting it (e.g. you previously owned one back in the day, which it sounds like you did not). When I get to my magazines I'll be happy to send you scans of ads and any specifics which I find. And do please forward photos if you so choose. Depending on the colour of the paint, I may be able to place it to a certain year, in alignment with the paint options offered at the time.
Cheerio,
Peter Jourdain
Whitewater, Wisconsin USA
[edit]
Have been
> offered a Hercules Kestrel frame. Anyone have an idea of
> what to offer?
>
> Thanks
> Neil