The 221 c.i. V-8 has 24 studs per head. The smaller V8-60 has ?17? per head. I'm pretty sure though, that the smaller V-8 was not installed in '40 trucks, rather, the 4-cylinder (tractor) engine was used.

Of note: 39-41 BIG trucks had a 239 c.i. engine, designated the 99T. It has a slightly raised surface for the intake manifold.

It's very possible that your truck does not have the original engine, in which case, the only sure way to determine the displacement is to measure the bore and stroke.

Mike