Yup, sounds like a JG Regulator, and Dave Lindsley sells the current versions. If it is, the dynamo does need slightly modding as John says, to what I call 'Miller' spec for shorthand.
The field coil wires that emerge through the brushplate need to be connected one to F (as always) and t'other to D. Ie, the one that would be (is, even?) connected to earth along with one brush needs to be swapped to D, with the earth brush tail being the only thing that is then earthed. And you'll need to check the rotation if there's any doubt.
I've got a 12v one of these, with blue for D, green for F and black for A, positive earth through the mounting stud(s) - my one has 2 studs. It worked fine for 20 years, and only got replaced because I like DVR2s. If you send me an e-mail address, I'll send you the original (type-written!) maker's instructions for the version I have if you want them. It includes pix of the brush plate etc as wired correctly.