Yup, quite a few ohms there but 'tis true Trev. No idea of wire thicknesses or number of turns though. Std field coils I've got are indeed 2.7 or 2.8 ohms. This aftermarket so-called '12v' field isn't 'made here' - I bought it from Feked in the UK I think, along with a finer-wound armature allegedly made to go with it. In combination they've been OK, but strictly limited in power to 60W or a flimsy 4.5A-ish at operating system voltage. Cut-in supporting a 12v system is not far off tickover. Nice. It reaches its fully regulated state by about 1850 rpm. Nice too I think, from the windings' point of view because the thing is running fully regulated for most of the time out on the road.
By contrast, my 'std wound' set-up supporting 12v kicks in at higher rpm, and doesn't get to a state of being fully regulated until well over 2000rpm. This obviously implies some burden on the dynamo under full loads at lowish rpm. However, the windings would be happy to take as much or more current at 6v, so OK so far. This is actually my favourite dynamo option in winter (it was -5° this morning here), as it is robust (25 years on the same dynamo guts says it has to be) and supports a 35W halogen light plus some Oxford HotHands which use 32W (a concession to thickening knuckle joints). 72-75W seem quite supportable continuously without stressing anything unduly - 80W? Hey, maybe! In summer it supports a 60/55W halogen easily. No other dynamo option I have in my shed can do these things, and some smaller alternators would struggle too, what with ignition loads to worry about on top.
Both these 12v options are imo better for night work than the std 6v system on my A, although that's not at all bad, especially with belt drive.
The funny thing is, when I was young I could see in the dark . . .