I still think it's tempting to suggest Gibson might have done this sunburst as a custom job.
I've been comparing it to the EB-3 (1963 sunburst) from the flyguitars site (borrowed a pic.)
and the colours are very similar. Even that checkering is the same, with that large pattern.
Of course, it does not prove anything, BUT the EB-3 is also possibly converted from an EB-0, by who? Gibson?
It sure is a rather professional routing job, and given the obviously old refin, could anyone buy Gibson bass mini-humbuckers
and also the GA-90 1C coil if they wanted to convert their EB-0's? Does not sound likely to me.
Of course, these days you can buy any part you like at any time if you got the dollars, and to learn
som 'quick checkering jobs' and ageing stuff is done rather easily on the internet too..
Maybe some punk's got a gibson sunburst shop in the basement, ageing cheap epi's??