In helping a friend find a matching-numbers 1969 Triumph Bonneville or TR6, we're4 getting conflicting information about the downtube where the serial number is displayed. Several bikes we've seen have frames with a flat spot that has been ground into the downtube to accomodate the serial number, which is very different from frames that have a raised boss that was cast into the frame so the number could then be stamped in.
Even so, we are told by some reputable sellers that the ground-in flat spot was indeed the way some early-1969 Triumph frames left the factory. Is it possible the Triumph factory had varying practices when it came to displaying frame numbers?
Any guidance you can offer is appreciated. Just trying to help a friend find a legitimate bike with matching frame and engine numbers the way Meriden intended. With the way prices on these bikes have escalated, it's important not to make a costly mistake.