Pete,
Before you get ahead of it all, keep in mind that while the little Gennipod isn't "designed' for 110 mph, it's because his airplane and those around him cruise at 75, and his own amp load is 4 amps or less. He designed to meet his goal. So, if someone wants to test one for awhile north of 100 mph, one may find that it's a prebuilt solution that would suffice. And spinning faster will probably get the amps up over 6 as well. He uses a solid state regulator too. For my own 90 mph and lower draw, the Genni would probably be the smart way for me to go, and it would probably work fine. But I like different mousetraps too.
So that said, yes, I can spin it on a drill press, but I'd need to understand how to measure the output with a meter and no load. And is this with a regulator inline, or just the dynamo?
I've thought about the prop used for ag pumps, and I'd sure hope we wouldn't need to get to that point. That size of a prop would probably not be of interest to me, between the logistical size, aesthetics and most importantly, the drag aspect. There are a number of small outboard props that may be of a suitable diameter, but my guess is they will be too flat of a pitch. Piranha props offer a nice composite prop with interchangeable blades on the hub, there by allowing different pitch props. I've not looked up what pitch range they offer.
When you're spinning the prop, you provide torque with a flat, low pitch prop. When you're trying to extract torque from a spinning prop, you need a course, high pitch prop. And most small outboards don't have the hp to drive a high pitch prop. One option is to take a larger high pitch prop and start cutting down the blades to get the diameter you want, while testing to ensure it keeps spinning the unit.
If you want to do some online homework, see if you can find a multi-bladed (think axial flow) fan blade, or as he calls it, an impeller, with a 4-6" diameter.
Other aspects - Probably need to machine a replacement shaft with provisions to allow a prop flange, or mounting method. The current flat head provides no attachment means that would ensure alignment.
pb