That's because cheap bastards like me are always looking for a way to avoid paying someone to do things for them or buying expensive equipment that is seldom used. But that is a cool calculator.
A hole saw and a cheap notching clamp is all you need, and a selection of hole saws to match the dia of the tube you want to notch, from memory mine cost about $70, just bolt it to your drill table insert hole say and away you go.
I knew about those John, but I was looking for a way to do maybe a couple of fits one time. If I was doing the complete chassis type stuff that you do I would buy a nice tool like that. Good additional info for this thread.