H.I.,
I beg to differ. Staggered bolts on valve cover came till 59, also on 283. One other trick is the lack of side bolts bosses on the 265 only. There were 283 made in 57 that also lacked the side mounts. If it has side mounts it is not a 265, but if it lacks, can be a 265 or a rare 57 283.
