On Jim's guitar, Gretsch didn't make a RocJet until the early 70's, so the source that had it as a '63 was erroneous. Gretsch did produce a series of Les Paul-shaped semisolids under variations of the "Jet" name starting as early as '54 (Gene Vincent's original guitarist Cliff Gallup and Bo Diddley both played them in that decade), and may have still been producing them in '63, but that was about when they were discontinued. The later RocJets, made after Baldwin had bought out Gretsch, were slightly differently shaped and had a Gibson-style controls layout and different pickups (all humbuckers, I think).