This is a great idea and a very nice design. Thank you for this.
I used TPU at 70% infill instead of PLA and it works great.
Posted it as a make first but decided to post it as a remix due to the new magnet size.
Magnet inserts are 12.2mm x 2.2mm for 12 x 2mm magnets and the inner distance for the jaw is 4" for a 4" vice.

Creality

Ender 3 Pro

No

No

.2

70%