Having grown up around them, seen countless hopped up engines, even seeing several blown and/or injected rails run back in the '70s (when you could still find the occasional flatty on the strips), and just recently visiting the Early Ford V8 Museum, which had tons of stuff that I had never even seen in all the vintage '40s-'60s mags that I grew up with, I've never seen a rear dizzy flathead. I'd think it would have to be using a billet cam to get the gear drive on the rear, so it'd have to be some new concoction that somebody has dreamed up.
I don't see any advantage to it. In fact, I'd think it'd be worse. The original dizzy is driven off the front of the cam, where the gear drive is, so there's no added twist to the cam that might be imposed on a rear drive. Even an Ardun has the front drive with those huge heads. Superchargers don't even come close to causing an issue. I just don't see the point unless that front engine space is being used for something very outside the ordinary.