British lower range frame - Falcon, Viking, Sun or maybe Carlton from the late 1960's to 1971/2. Does it have any serial numbers or stampings on the frame? It looks like you may have a problem if that's a dent at the rear of the head tube. Check it out from the inside when you remove the forks to work on the head set. It shouldn't touch the fork steerer tube on the inside and it would be a good idea to ask a couple of proper bike shops for their opinion whether it is likely to have weakened the frame? NOT Halfords or Cycles UK! Evans, Holdsworth or similar outfits will have the expertise. I'd guess it's probably be OK and if so it might push out or fill (or both). Unusual place for a dent though. Powder coating will certainly give you a tough finish, although with that graceful seat cluster and sculpted fork crown, my own preference would be for a metal flake metallic finish with deep lustre lacquer - mid blue, crimson or gold perhaps? Anyway, you have the basis for a nice build if the frame's OK so good luck and keep us posted on how it goes!