Here's another shot of probably your best option, which is the stock Schwinn pulley; it ain't pretty but it works like a champ. This one's on a Mesa Runner, brakes are cantilever. I'd wager you can find one at your local co-op for a buck or two.
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A race bike in any era is a highly personal choice that at its "best" balances the requirements of fit, weight, handling, durability and cost tempered by the willingness to toss it and oneself down the pavement at considerable speed. ~Bandera