My 56 3100 has all 3/16 lines. I replaced lines on a 56 3200 for a customer and they were as you described 1/4 except the rear axle housing. A 3600 has 1/4 lines throughout. I think it is a long bed short bed thing. 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
