I wish you luck with the search, but it is again imho a lost cause because there is now no cosmetic connection to aid in establishing any kind of provenance for this particular amp even if those close to the situations back then recalled Allman using a brown covered 2x10 Fender amp. Now, if there was a tech who had documented the amp by serial number and that tube chart, THEN you would have provenance. it is however an interesting story.