1.) 3.1 uses a nut/screw as the top battery terminal, 4.2 uses a standard bat contacts
Mouser Electronics - Electronic Components Distributor
2.) 3.1 uses 2 insert fasteners with screws, 4.2 needs 4 sets
McMaster-Carr
3.) 3.1 uses two magnets, 4,2 uses two sizes of magnets, 6 top and 6 bottom
Top: https://www.kjmagnetics.com/proddetail.asp?prod=D26-N52
Bottom: https://www.kjmagnetics.com/proddetail.asp?prod=D24-N52
You can source them individually but it might be cheaper to get the kit when you figure in shipping
Mouser Electronics - Electronic Components Distributor
2.) 3.1 uses 2 insert fasteners with screws, 4.2 needs 4 sets
McMaster-Carr
3.) 3.1 uses two magnets, 4,2 uses two sizes of magnets, 6 top and 6 bottom
Top: https://www.kjmagnetics.com/proddetail.asp?prod=D26-N52
Bottom: https://www.kjmagnetics.com/proddetail.asp?prod=D24-N52
You can source them individually but it might be cheaper to get the kit when you figure in shipping