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...I just recommended the SRAM two speed hub to some one else and am using one on a track bike build to get around the not drilled for brakes on a track bike thing. You can buy them with or without a coaster brake, and run them either 120 or 130 spacing.

Amazon.com : SRAM 36h Automatix 2 Speed Coaster Brake Rear Hub : Bike Hubs : Sports & Outdoors