Cropping modern video to older aspect ratios?

I have an old Mac tower with Final Cut Studio on it that works fine for video editing. It still produces nice videos using FCP7, and I know how to use it.

What I’d like to do with this setup is create a simple video that compares some old family photos that I have to the same locations where they were taken, showing how those locations look today. In other words, I would walk with a videocam to some place where an old picture was taken, pause and aim it at the exact spot, and then fade into the picture that was taken there long ago.

Trouble is, most of these old photos are scanned slides, and these images have a much more square aspect ratio (I’m thinking 4:3) than images produced by modern still cameras or videocams. All the modern cameras produce widescreen only, especially the videocams, which create such wide video that I’m guessing they’re meant to conform to the shape of modern wide, flat-screen TVs, or cinema screens. And none of these modern videocams that I have, or have seen, can shoot in 4:3. It’s not an option in their menus. They can only produce widescreen video.

So my question is: if I were to take take modern video of these places, using a current videocam, is there some way that I can crop that wide video down to the same aspect ratio as the slides, either in FCP 7 or some other app?

I have older tape-based video cameras that can do the 4:3 aspect ratio, and I suppose I could go back to using those cameras (if the batteries are still any good), but I’d rather not go back to tape if I can help it. For one thing, tape is painfully slow to load video into final Cut, compared to just dropping in a video file off a memory card.

So, I guess I’m asking whether modern widescreen video can somehow be cropped or edited down to 4:3. Does anyone have any ideas how I could do that?