[mr48chev]

That block casting was available from 58 through 61. That is why "some say". Chevrolet casting numbers for a certain size engine usually run for several years until a major change was made in the casting. On that block it means a 235 with side mounts.
On the code stamped on the pad by the distributor the F means that it was built in Flint Mi the J means it's a truck engine.


There is also a casting date code on it that tells you pretty well when the block was cast.
The casting date code for the block is located behind the starter.



The first letter stands for the month { A is January - L is December}
The second number is the day of the month
The third number is the year.