maybe he owned it, maybe he didn't, but JG is not relevant enough to effect the value of that amp. If I were going to lie i'd pick a more famous dead person, that didn't die a couple days before.
If it were a Blackface * Vibrolux * Reverb, owned by just your average everyday commoner, 3K is not so unrealistic to be honest, would have easilly gotten that a few years ago. with patience could still pull that. the Twin though, is just too loud. way too much supply, much less demand in comparison. could prob get a nice silverface twin reverb for 500 on a good day.