I'd spread the rear to 126 at least... you can run 7 speed cassettes or a freewheel with modern shifting ramps and the friction shifters will work perfectly fine. I somehow broke the indexing on my bar-ends and I shift 9 cogs in friction mode, besides on tour I don't find myself shifting all that much anyway. I'd be more inclined to invest in a 135mm cassette wheel with 8 or 9 gears... I'd guess the DB frame could be spread that far without issue... I'd keep the friction shifters too since I'm a simple dude.