The pickups are generally set up for a particular pan. The best example I can give is the passenger cars. 55-57 pickup is slightly different then a 58, and the 59-63 is different then the 55-57 and 58 pickups. So the question is how positive are you that your block is a 56 production block? Any chance its a 54 early 55 style block cast in 56 as a service replacement? Any idea of what pan you are using? The 54-early 55 pans are slightly different then the later pans, and I am not sure of all of the variations of truck pans, if there are variations, from late 55 through 63.
