I have a B350 and while looking for the io shield I happened to notice the B450 is very similar only difference is B450 is missing VGA and has a USB C instead of 2 USB A.
Just copied one block of USB ports and moved it over a bit same with the DVI port copied and shrank it slightly.
b350primeioshield.stl | 324.0KB | |
b350primeioshieldsame-thickness-as-original.stl | 305.8KB |