If you want to get technical, you can pretty much freely swap engines between any 911 built between '65-'98. And if you want to do the plumbing you can put a water cooled version in an early car as well
The Rolex analogy is flawed though, because a camera produces a subjective output (a photo). Time has an objective measure. With a Rolex (or other "nice" watch), the intangibles are the quality of construction, engineering involved, style, flash, etc. I can appreciate the marvelous build of a Rolex automatic, but realize that it won't keep better time than a Timex. The Rolex however isn't a disposable item, can be fixed, doesn't require batteries, etc. So there are a lot of factors.
For the record my ex gave me a Rolex Explorer 1 about 10 years ago. I actually don't wear it (or any watch), but do appreciate how cool the movement is. I wouldn't buy one for myself though...other things I'd rather spend my money on.