235 vs. 261 doesn't matter.
What matters in what year the cylinder block is because they changed the way oil gets to the top in 1958. 58-62 blocks use 58-62 arms. 53-57 blocks use 53-57 arms.
The difference in arms is the inside annular groove.
58-62 are offset, 53-57 are centered.
The size of the grooves are different also. If you try to use 53-57 arms on a 58-62 block, it will put too much oil upstairs.
