I've just bought this bike. Anyone know the history?
Possibly noone knows more about it now than you and the fellow you bought it from. However, reaching out to the good folks at the UK Royal Enfield Owners Club as David Blasco describes in his blog at
https://royal-enfields.blogspot.com/ (view as "Desktop Version" for best results) may be fruitful if you provide some obvious data like engine and frame numbers and maybe the photos already shown here. Here's an image of David's tip:
You might also try reaching out to Hitchcocks about its provenance, since it's highly likely whoever cobbled it together may have been a big customer.
If it runs well, I'm with 'Narada': Who cares if it's not "original"? That's one pretty bike. There are lots of bits that obviously didn't roll off the line at the Redditch factory, like the fuel tank, which is pretty clearly off a pre-'96 Indian Bullet or an aftermarket replacement of same. And that rear carrier is a bit anachronistic--though my hunch is you may well learn to appreciate it while touring. Yet I also see the telltale signs of very great care to detail in those gobs of pricey stainless steel and other top shelf bits having been used, and I can pretty much guarantee you'll be happier and she'll run sweeter with that 1-into-2 intake manifold and single fresh-looking Amal or Wassel Concentric carb than a pair of worn out or leaky Monoblocs, or whatever she originally came with.
If you paid less for it than for a new 650, then I'd say you probably did well indeed.
Personally, I'd love to see a quick YouTube of her starting and maybe running down the road a bit, if you could manage that.