I recalled reading recently that the pre-Advance-Design trucks might not have had a straight-through muffler, so I looked at the Shop Manuals.

1941 truck muffler " . . a new unit muffler of integral construction, employing reverse-flow and diffusion principle used so successfully on passenger cars to obtain quiet operation".

If you interested in it being OK for driving: as crenwelge posted, the later straight-through design will work fine.