Yeah, looking at the plate it looks like a Dyna 3, they were a really good ignition, I've had a couple over the years and they chucked a nice fat blue spark. I don't know why Dyna stopped making them, except that they were about twice the price of the Dyna S.
I've got a very trick Gerex Multi Spark ignition for a GS1000 here, they went broke because they were awfully expensive, but were supposed to work well. Cheers, Terry.