Which direction do your throttle shafts rotate? Parallel or perpendicular to the long axis of the engine? Do you want to use stock linkage or a straight aft pull? I just completed a 5 X 2 progressive linkage on a 261 with five Strombergs, using parts on hand and from Charlie Price's Vintage Speed. My throttle shafts are perpendicular to the long axis of the engine, so that made it fairly easy to adapt a V-8 3 x 1 design.
linkage
