Probably not. There are several differences between the original 500/600MHz PowerPC 750cx-based models and the later 700-900MHz 750fx-based models, mostly the heatsink and maybe a few random screws, in addition to the fact that the little cooling fan is a totally different style with a slightly different mounting scheme. You may be able to rig something up, but it may be more work than it's worth. Besides, the later models are notorious for the GPU problem.

If I were going to do anything, I'd just upgrade to the 600MHz version and call it good. There are enough improvements from the 500 to 600MHz models for the transplant to be noticeable, and the boards are completely compatible with one another.