1. 54 cars & 54/55st trucks - 4 vent slits in the top, non-vented oil filler-cap in front
2. 55-58 cars & 55nd-1963 trucks - no vent slits in the top, vented oil filler-cap in the front
3. 59-63 cars - no vents in the top and vented oil-filler cap in the middle
I am most likely wrong on cars/trucks being different in 59-63. However, both of my 1960 and 1959 261s both had valve covers with filler in the front.
Tim, I have seen a few '59 trucks, plus 1 '60 with the 3rd style cover with the filler cap in the middle. All were spotted in local salvage yards, but as far as I know, they were still original to their respective trucks Nothing seemed special about the engines, no unusual equipment other than one had a governor on it. The '59s were a 3800 flatbed and a 4500 School Bus, the 60 was a C60 with a 261 (yes, I regret not grabbing that engine).
