Very nice Andy, I've got the (most collectible) 1979 "small port" GS1000S in bits, (retirement project) and a 1981 GS1000S as my daily rider. (plus a GS750E, GS1000E, and a GS1000G)
Great bikes, excellent brakes and handling, with bullet proof engines. Even the "softer" US market CV carb equipped models, (EPA enforced, other markets got big Mikuni 33mm slide carbs) can do 145+ MPH.
Do yourself a favor though, if you want to go fast, take the OEM fairing off and hang it in your garage, it makes high speed riding scarier than it should, with poor aerodynamics inducing "tank slappers". I don't know anyone who rides his fast, who didn't take the fairing off.
Have you visited "The GS Resources" yet? I'm "Terry" there, and I do oil coolers for GS bikes too. Cheers, Terry.