Your cab (imo) is a 1960a. Black cloth was introduced in '75, but I'm thinking the top skid trays were a little later as I don't remember them on a 76 cab I had?
The weird thing for me is your speakers?
T1281 is a 15 ohm, standard 60cs speaker introduced in 1966 onwards... BUT your date code given, 12LA is the 12th of April 1963
The next time Celestion reverted back to this format of codes was in 1992, which would make them '92 speakers... BUT you have black tab boards on the wire connectors which were changed to grey from 1970ish to date???? all seems very strange, anyone shed any light?
Btw. do you have any cone codes (white numbers actually printed on the paper cones)?