Mike: The pre-war "long" action is different from the post-war guns, in that the hammer and sear arrangement is different (rebounding hammer block)and post war guns are generally called 'short action' and have an "S" serial prefix. Older long actions are identifiable by the shape of the hammer. Some early post-war "S" serial number guns have the long action (or some other features) and are called 'transitionals', and like SP said, can be rare. Generally made in 1947-49 time lines.
See the shape of the hammer, how the spur is much higher? On the post-war guns the spur "sprouts" from near the middle of the hammer rather than near the top as on the pre-war guns.
Also note the "dimple" under the cylinder release. The pre-1945 frames have this feature. Easy to spot.
Another example:
These pre-1945 guns are called the "long-action" models. The transitional guns were those assembled after 1945 (up until maybe 1947) using left over parts from before the war. So they have the long action but have post-war serial numbers.
These are fairly rare and of interest to collectors. Look for the one-line S&W marking on the right side of the frame. True post-war guns have a four-line address.
Mike,
Without pics and other info and assuming it is in the 74-75000 range with a standard ejector rod, 4 line address and pre war style hammer, 95% condition, $500 is not a bad range to start with. This could go up or down depending on condition.
Hope this helps,
Bill