I might have to agree with Jerry. The terminals on that switch look a little small. But not knowing the specifications on Crummy's switch, it might work just fine. The biggest issue with switches (or relays) and their rating is the ability to disconnect with power across them, which isn't really an issue with a battery disconnect as you wouldn't normally disconnect with the starter engaged. But it's something that needs to be paid attention to.
[on edit] looks like hcb3200 got there first with the correct info.
Another thing to point out is to be sure to provide some protection for the cables where they go through the sheet metal of the floor. Use a grommet or a nice thick sleeve around the cables - especially if you're bringing the positive cable thru the switch. Doesn't matter quite as much on the ground cable, but still good practice.
