There are no official 500 Bullets for 1967. The UK factory had ceased production and the Indian factory would not produce a 500 for at least another 20 years!
It sounds like this 500 is an unofficial import, most likely the frame off a 1967 350 (if even that is genuine) fitted with a 500 engine and more recent running gear. There is a whole industry in India selling these bitsas to unsuspecting westerners.
IF whoever brought it into Spain succeeded in getting it registered and there is full EU or at least Spanish-compliant paperwork, and IF whoever put the thing together did a decent job, it could still be a worthwhile motorcycle, you would have to do some investigation!
The 500 EFI would, I expect, be a more trouble-free purchase.
A.