Yup, I've done it more times than I can count. The 5400 and 6400 are identical, and the 5500 and 6500 are identical. So I've often popped the 5500 board into the 6400, and vice-versa.

Other than a speedbump, graphic, and memory differences, power requirements and all that are pretty much identical with the 5/6400 and 5/6500 series.