Once upon a time someone posted that Fairbanks Morse made the Rupp units, but I've never been able to confirm that anywhere.
OP, If you're not happy, then let the seller know. It'll come down to you and him working it out.
For some reason, I thought it was the 12 o'clock orientation, but I was wrong. From what I was told years ago, not having them in the right orientation on a slanted engine will cause damage to the blower housing. Here's the original engine from my 1970 Rupp
you can get 1/4-20 studs on...
I don't know for sure. I know it was offered as an option from Rupp originally, but I recall someone saying they eventually made it standard because it was the only way to get enough leverage to make it work
The engine looks like it could be original (no starter mount, no fuel line holes in the blower housing) but the serial plate is missing and I'm not seeing the lighting coil wires. My guess is someone either replaced the engine or at the very least, replaced the flywheel/coil