dual shaft isn't an issue. you can start the motor and put a hacksaw blade on the second shaft to cut it off. There's probably more elegant ways to delete it, but that's the simple way.
snow blower Tecumsehs will need a new carb and air cleaner. and may need a new oil dip stick (if it currently has that long set up.) I recommend the inexpensive ebay $10 carb. It work well and it's cheap. The most expensive part is the mini bike style air cleaner/filter. Those run about $25.
as for the PTO shaft, you really want a 3/4" shaft with no taper. it will need to be drilled/tapped at the end, but you can do that. Length should be 2.25" (or longer). A 1" shaft will work too. But you can't have any taper on the PTO, it has to be consistent. If it has a tapered shaft, you'll need to replace the crankshaft (or have it made consistently 3/4" on a lathe, and a new key slot cut. that's probably outside the scope of what most people want to do.
you will also need a mini bike style throttle linkage. You can buy that from OldMiniBikes warehouse for about $15.
To make it work on a Rupp, depending on the model, you may need a slant intake manifold. You can get that from Black Widow Motorsport for about $40.
I have a thread on all this stuff if you do some searching here. I believe the title of the thread is, "restoring a tecumseh, another way"
https://www.oldminibikes.com/forum/mini-bike-discussion/159401-restoring-tecumseh.html