Drivetrain right angle gearbox question
 

First time on this site, so I apologize if this is a misplaced thread or anything.

I have a 1997 Hyundai golf cart that I'm converting from electric power to gas, and I'll be using a way overkill (I live in a small town and this was all I could find) 16hp lawnmower engine with a vertical shaft that I need to convert the rotation from to a horizontal input. I already have a transmission installed and ready to go, and the engine is basically complete. I just need a 90° gearbox that will take a maximum RPM of 3,600 or more that has a female 1 inch bore so it will slide onto my transmission input shaft. The plan is to use the pulley that was originally for the blades to drive the transmission through that gearbox and via a belt, so that it will slip instead of destroying the drivetrain.

The problem is that I literally cannot find any gearbox online that can take over 3,600 RPM and has a female 1 inch bore, while also being small enough to fit into the tight spaces. Any help would be appreciated.

I posted a picture in the attachments. The green shaft on the left is the transmission input that the gearbox needs to fit onto. As you can see, there's not much room for it. And yes, I promise it's temporary. I'm just trying to mock it up so I know what parts I will need in the long run. You can see the black engine pulley on the right that the gearbox needs to go down to. I plan on attaching a shaft to the input of the gearbox and putting a pulley on the end to connect the gearbox and engine via a belt. (Again, temporarily, for mock-up.) https://imgur.com/FyBrFPi

Welcome
I see you're space constrained! Peerless made a vertical to horizontal gear box or a 90degree (I actually owned one back when) that came in a lawnmower (I think a Wheelhorse). Don't remember shaft sizes but such a thing did exist. It wasn't very big & it was at least rated for 3,600 rpm.You might have to put a pulley on the gearbox too & have 2 belt drives before the gearbox/CVT, problem would be length of those belts-very short!