Battery question

I hate to seem stupid, but I purchased a new Delco battery for my '67 El Camino, and when I tried to install it I noticed that the old battery had the negative and positive terminals on opposite sides from the new one. I didn't think there was any difference from one original-style top-terminal battery to another. Is this possibly some sort of manufacturing defect? I know I can't install it backwards, and the cables can't be switched from their proper positions. Any suggestions? This seems really strange to me. Thanks.

Batteries are made in a variety of shapes, and with the two posts located in different orientations. Either you got a battery from the wrong 'group', (which is how the different styles are designated; group 42, group 27, etc.) for your car, or someone changed the original battery cables. That would be likely, as battery cables lasting 43 years would be too much to hope for.
Sometimes the only difference between one battery group and another is where the positive and negative posts are located. Other differences would include the battery being too long or too wide for the battery box, or too tall (danger of the terminal hitting the hood, or just being larger in volume. They also come with different ratings for 'cold cranking amps', but this is more related to how they are constructed inside rather than to the size/shape/weight.
So you could change to a battery having the terminals where they can be reached by the existing battery cables, or change the battery cables to be slightly longer.
Personally I always buy the least expensive battery that isnt made for a riding lawn-mower or motorcycle. They last about as long as the ones "guaranteed" for 70 months or 80 months. I put 'guarantee' in quotes, since my personal experience is that once the battery is over two years old - its hardly worth pursuing the guarantee if it should go bad.