The 1980 and 1981 GS1000 8 valve engines came with an excellent factory electronic ignition mate, but to convert yours you'd need to also change out the wiring harness, so you're better off just buying a Dyna S from Z1 Enterprises, they're about the cheapest and Jeff Saunders, the proprieter, is a member here.
The GS1000 is my other infatuation, I've got a 1979 GS1000S, 1980 GS1000E, and 1981 GS1000S as well as a couple of parts bikes, they are a fantastic bike, and are well catered for at "The GS Resources" website, my GSR user ID is "Terry".