Vintage Thing No.88.1 - Gregory Special

It's an AMC gearbox I knew my mates would oblige with identifying the gearbox on the Gregory 500. Pete Low has come up trumps but is just as perplexed by the Gregory 500 as I am. Not only that, but he's mentioned another weird and wonderful machine by the name of George. Here's his e-mail to me in full. "I've never seen this bike. The engine looks Jawa to me, from the timing side, with its exposed oil pump, but I agree that the timing side is weird. "A mate of mine took over a thing called "George" (after its maker) it was a BSA B31 with a Jawa engine grafted in, but I remember it used a timing side cam drive that made use of the Beeser's alloy push rod tunnel. Now that's got me wondering. Was it a Jawa bottom end with a BSA head? or vice versa? Sorry can't remember! "The gearbox is simple. AMC type, as used by AJS/Matchless/Norton from mid 50's to the last of the Norton Commandos, and the clutch goe...