From 1942 thru 1948 they are wider by an inch and a half or so. If the tag is still on it, it should have the last two digits of the year with a prefix F for Ford, M for Mercury, or LZ for Lincoln. Parts can be mixed & matched though so there is no guarantee even with a tag. The 35 & 36 should have the bone mountings that were mentioned previously plus mechanical brakes. The 33 & 34 are very rare and the 35 & 36 are not common either. The 37 thru 41 are more common but the 42 thru 48 are the most common and are the wide ones. The wide ones will work on an older car but the wheels will stick out from the body a bit more. Some folks modify the wide ones to work on the earlier axles but it takes someone with a jig and some experience to get it right. Bullet proofing one is a good idea. Some of the parts are weak and should be reinforced before they crack. The Columbia mod can get expensive but they are really nice on a period correct car.
http://www.columbiatwospeedparts.com...r-columbia.cfm