HI diyjonesy
Firstly are you reading the frame number off the bike or the log book, it is possible that the log book number was written wrong.
The frame number on the bike should be found on the fillet that wraps around the headstock at the front of the bike (left hand side sitting on the bike)
Frame numbers for 1961 run from GA7-11101 onwards to GA7-21120 (1962) so several possibilities with your GA777167
Check it's not any of the following - GA7-7167, GA7-17167 you get the picture? sometimes the stamping is a bit obscure , frame may have been heavily painted, frame might have been damaged and replaced with new in which case the Dealers were supposed to stamp the original number on the new frame but mistakes might occur and so on