That case looks similar to the one for the Epiphone Crestwood Deluxes. I know it fits in those, but the neck is resting way up high and that makes me nervous. I have a friend who has one of those, and I have been tempted, just because it's better than what I have right now.
If you have a line on the 60s blue lined crest wood case I would snag it! I believe that is the OHSC for the thunderbird! Even if you are not comfortable using it 100 percent of the time, if you have the thunderbird you should snag that!
As as for the Epi bass case I referenced , as well as the guardian tweed bass case, they fit my Jetstars pretty good, and I am pretty mental about how my guitars fit (or don't fit) in their cases. With that said there is some extra room with the Jetstars in those cases, but overall I'm comfortable with the fit for my purposes. I also have one in an older obscure TKL guitar hard case that was likely for a Gibson firebird/ thunderbird. So a modern version of that may work for you. And finally, the MONO M80/M80 Vertigo hard/soft case works for the 1966 6-inline headstock jetstar. Never tried the other w the thunderbird headstock but that may work as well.
not easy guitars to find cases for!