interesting bit of Shimano:
It’s cool … but it’s only a triple-izer middle ring (not original or using a different smaller bcd). But it’s there and not a bad price. French pedal threading to 9/16" standard takes only a minute or two and is easily done for those who might be put off by it.
Shimano 600 but a little more interesting is the “touring” series they introduced in the mid 70’s (not sure of dates). It used a 3 arm crank with a small bcd but i’ve never seen it with anything other than 40+ tooth inner rings which makes it not very “touring” imo. I also thought the chainring’s looked a little funky/too busy but I was lucky enough to entrust John Bosevski from Cycle Underground to make a few specials to suit this crank that I thought more useful gearing wise (30/46 instead of 44/53) and perhaps a little better looking. Good man John 
… not much point in programming his CNC machine (?) for a one off 3 arm crank with a proprietary bcd but he did this one set for me for which I was very grateful (and paid extra for his time which is only fair).
http://velobase.com/ViewComponent.aspx?ID=4BC1BB89-8749-4F24-AB72-2C3CBB7DAB42&Enum=115&AbsPos=2
^^ nice work.
Thanks, and props to J. Bosevski for entertaining my grand ideas. In reality I’d much advise others to buy ready made Stronglight/Nervar/Specialites TA 3 arm alloy cranksets for cheap as 28/32t small rings are sometimes available for them … or just buy the re-issued/remade Herse cranks just beautiful. They make great touring double’s with wide range 8/9/10 speed rear cassette’s.
btw, Campy made alloy 3 arm cranks but not many chainring options and way too pricey to be practical imo.
And here we have them;
Shimano R600 Crankset cranks 1984 vintage 50T / 34T tooth fixie road bike | eBay
That big chainring on the tiny BCD looks like it would fold if you put the power down!