Re: YIKES ... '63 Bassman
One other thing....the plastic dogbone handle was not original equipment. Fender used the leather with the chrome end covers. You can see evidence of that handle on the spkr cab. Also you can see, by the screw holes, that the original handle was at one time replaced with a dogbone and then removed.
And since you cannot see any evidence of the original handle ends on the top of the amp, then you must conclude that the top tolex piece is also not original.
I am certainly not an expert on vintage amps, but I did live in this era and owned two early Fender amps (one was a '62 small vibrato combo, don't recall the model, and one was a '66 Bandmaster which had the same hardware as the Bassman).