As you all know, I'm relatively new to the world of Vincent mystery. However, I have been dealing with a gear selection problem over the last couple of weeks and I'll run through the sequence just in case it's of help.
When I first started riding my Rapide after a full restoration I found that gear selection was a problem. I found that I could adjust the G59AS to give equal clearance top and bottom in second gear, adjust G49 appropriately (after taking the eccentric bit out, smoothing it off and greasing it to work easily) and this allowed selection of gears 1,2,3 and 4 in that order fairly reliably. I could not get changing down 4,3,2,1 to work reliably at all. After some messing around, I found that the G64 spring had a lot of play so I tightened the small end to reduce the play. Still no good. Some reading, asking about etc., revealed that it was possible to over-select gears - i.e. the travel of the gearlever was too much to select the gears accurately on the way up. I was told that there was a G61 mod (G61/1) that provided an ear on each side that limits the gearlever travel so I ordered one from the Spares Co. However, when I tried to fit this the right-hand ear fouled the kickstart quadrant and prevented full movement of the G61 to the right - my G61 has to be quite far across to the right to achieve the correct adjustment. I checked the dimensions of the G61/1 and it was wider than the original G61 (this is now being addressed by the Spares Co - thanks Ian). My solution was to make an ear and weld it onto the left side of my old G61 and, after setting up the G59AS and the G49 again, this has now cured the over-selection problem and the gears select correctly. In my case I don't need a right-hand ear because the kickstart quadrant effectively limits the down travel of the gearlever as the G61 is fairly far over to the right.
I suspect that those who have ridden Vincents for a long time are used to feeling the gears in as opposed to expecting the box to function like a modern box. I hope this is useful......