Engine code F425B breaks down as follows,
F = Flint Engine Plant
4 = Month (April)
25 = Day
B = Passenger car 235 with Powerglide
Like Bill said, it looks like a 1959 block with a 'I 1 0' date code on the Head (Sept 1, 1960).
Note, Chevrolet stopped putting "serial numbers" on their engines at the end of the 1956 model year. So, you have casting numbers for the part number and date code as well as misc. numbers used by the foundry in the process of making the casting.
Mike B
