I happened to have a bi-metal holesaw that a buddy and I used to de-baffle his motorcycle.
However, you don't need anything that big, really, assuming you are using the March pump. IIRC, you need unremarkable small bits for the screws, and something in the 1" range for the "dimple" where the center shaft goes through.
I've got the pump, a PID, a contactor (used as a saftey, no current to pump=no current to the heater) a fan that I still haven't hooked up, I forget what else. No SSR, as my element is only 200w, which the PID can pass through itself in relay mode.
If all you're putting in yours is a pump, it's a cakewalk.
My biggest recommendation is to mount the pump HIGH as you can. I'm going to do mine again, with the pump up as high as I can get it. Otherwise, you have the issue I have now, that the connectors for the hose on the bottom of the pump reach lower than the can itself. I just sit mine on another can in the meantime, but it would be nice not to have to.