Like the title asks: what kind of levers can I run if I want to use flat bars with sidepull calipers (Shimano 600, single pivot I think, not that it makes much difference)?

I have used mountain bike levers for flat bars, as long as they are for cantilever brakes and NOT for V brakes. I am using Nashbar "Jail" levers that are switchable between Cantilevers and V brakes. V brake levers pull too much cable and therefore don't give you enough leverage.

What vintage bike and Shimano 600 brake? If from the '70s, why not a lever from an old upright such as a Collegiate, Sports, etc. Both Dia-Comp and Weinmann made a nice looking alloy lever that polishes very nicely. The only picture I have of one is with this unusual Dia-Comp caliper.

I've used just about any non-V brake MTB lever with touring bars and old sidepull or centerpull brakes. Or I've used steel levers from old Raleigh 3 speeds. My favorites are Shimano SLRs, but really, even the cheap stuff seems to work fine.

Neal

I like the period-correct 4-finger motorcycle-style Shimanos on my mountain bike, because I can grab them even with my hands on the bar extensions.

thanks for the info. This is for a bike for the wifey. It'll be a bit of a frankenbuild, but should be reasonably light, solid, and right pretty. Further details as events warrant.