the code letters went to 3 letter starting in '70.
The casting date code is next to the dipstick.
CA comes up as a 1968 full size Chevy 250 with manual trans. per my Motors manual.
The reason the casting number says 230 or 250 is because the blocks are the same. The stroke is what's different, hence the difference in the top of the pistons.
A shallow dish to the tops of the pistons would seal it as a 250.
Or, you could drop the pan and check the casting number on the crankshaft as a last resort.
