Since the sum of the cubes of 3,4,5 equals 6 cubed, it is possible to have a dissection which builds either. See discussion here.
This dissection by Noam Elkies achieves the minimum number of pieces (8).
Printing:
The puzzle should print fine without support. STL files for individual pieces as well as the full collection are provided.
The author marked this model as their own original creation.