It is correct that FEA is a prefix for the 1948 235 (6000 series). Engine displacement is calculated using both the bore and stroke, and as Tim showed, both the 235 bore and stroke are different from the 216, so that's where the extra 19ci come from. The cranks for both engines have the same journal sizes--only the stroke is different. The connecting rods are the same, but the pistons and rings are different. The 235 pistons and rings are of course a bigger diameter, and the 235 pistons have a slightly different compression distance than the 216's.
I think the problem with many catalogs may be that they only consider the cars and light trucks (up to 1 ton). The 216 was the only engine available in the light vehicles until 1953, so some catalogs don't include the 235 that was only available in the 1.5 and 2 ton trucks before '53.
Another problem might be that the catalogs have the dates wrong regarding the availability of the 235. As one example, NAPA online doesn't show the 235 as available until 1952. In '52, they show it as available on the 3600 and 3800 trucks, which is wrong. For '53, they show the 235 as available on the 3100, and standard on the 3600 and 3800, which is also wrong. NAPA doesn't list trucks above the 3800. Another example is Egge Machine, a specialist in old engine parts. They don't show the 235 as available until 1950.
I don't think the year matters much, as all 235's shared the same bore size. As long as the piston matches the bore and the rings are correct for the piston. Jim Carter only lists one piston and one ring set for '41-'62, so according to him, one 235 piston fits all 235's. There were very slight differences in 235 rod length and piston pin diameter throughout the years, too, but that may not be of significance.
Edit: A 1964 parts manual shows replacement 235 pistons in two groups--'41-'53 and '54-'63. But certain oversizes are listed for all years.
