From the pitroad page, I understand you buy the $580 Warner synchro kit, and send them two shift rods for modification




The brass synchro rings are stock 60L items. But the cones are custom. Instead of being built into the gears it looks like they slip over the F5C56 gears

The hubs are also changed (may be stock 60L parts, or might be modified). GX-5 used triangular hubs




stock F5C56 synchros (GX-5 production)




A gearbox with this kit installed recently sold on Yahoo

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  F5C56 marked 'F5W56A'.jpg (47.40 KB)


  F5C56 gearset wih Warner synchro kit.jpg (45.11 KB)


  F5C56 counter gear SHIFT RODs.jpg (49.09 KB)