If you're going to go with a 1" bulkhead (1-3/4" hole for sched40 bulkhead) I can help you out, either lend you my bit or I could do the drilling. It would be the same size hole as what you have on your 20g overflow.
I also have 5/8" which is perfect for float valves (i.e. auto topoff).
I don't have any other sizes though. At the price of the bits I went with the two sizes I figured I'd use the most.
Kari lives much closer to you though than I do though
