Oooohh, that's right. I knew that at one point. I put this project on hold so long that I started forgetting things - I thought I needed to get an adapter plate, but I couldn't see why. I have a drill press, so I'll see if I can make an adapter plate myself.
Hole saws are not cost prohibitive, IMO.
Hey Diesel-Zuk - funny that we've got the same problem! I just ordered some steel plate and will try to make an adapter. What's the thickness of yours?