First, it would be advantageous to determine the years of your head and block.
- The head date casting codes might be found on the
top of the head, between the 4th and 5th cylinders' valve springs. (manifolds side of the head)
- The block casting ose might be found on the
lower left of the starter side of the block.- The engine ID is
pressed into the block in the ledge/boss to the left of where the distributor enters the block, As Hoyt stated, a 261 head and 235 block will bolt together, if they have the correct bolt pattern. Do they both have 18 head-bolt holes? If either has 15 holes, they will not bolt together and you are mistaken regarding the year of manufacture.
Even if you have 18 bolt head and block, it is not necessarily a "perfect match". They will bolt together, but you might have to make an adaptation to arrange for block oil to reach the rocker arms. (
see this discussion )
