H1 question

[McJamie]

I just picked up a 74 H1. In pretty decent shape, It'll need some cosmetic stuff, but no major mechanical work. What I want to do is keep it "period correct" as opposed to totally stock. So I am trying to hunt down the 2nd disc/caliper for the front( I think I have found a brand new one), and some appropriate tires.
My question is with the tires , what size can I put on the front? I can get Dunlop TT100's, but they list the front as a 4.10 x19. I'm wondering if this is too big. I know newer style tires will work better, but that's not what I'm trying to do with this bike. I can get a K70 for the front which is skinnier,and supposedly a match, but it's not what I want. I think (hope) it will fit, my dealer says he doesn't think so, but he's never even sold a set before.
Anyone else tried these tires?