I did the 3600 conversion after I did my 56 so I used mine as a guide. I have discovered that the after market linkage is assembled incorrectly. It has to be taken apart, then plug the ball into the pedal to determine which direction it pushes the lever, then assemble it and drill the corresponding holes. It's a little time consuming but it does fit and work.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine