Pakrat, the break point on the offset bolt holes in the valve covers was 1959. After that, all the smallblock V-8's had valve cover bolts straight across from each other. That would make the 265's, and early 283's the ones with the offset bolts. Also, the 1955 model 265 engines did not have a block-mounted oil filter. It's not a big thing, but if you're doing a restoration, that engine is HARD to find!
Jerry
