They used an Airheart hub/rotor as you’ll see in the pic

Here’s some additional pictures. The brakes are MCP. I thought the same thing that someone modified this for dirt track racing. There was a ton of dirt around the engine when I removed it.

It was located here in So Cal not far from Azusa.

Thank you Bob, I appreciate the info!

Can someone assist in identifying this Rupp, year and model?

Thank you!

Sold
Gentlemen, 1960’s Rupp go kart for sale

Thank you Rob. Ya they added a heavy steel plate on the back end. I told my friend that I’d see if I could figure out what it is so he can take it back to original if possible.

Pic2

Hey guys I just bought this. It had Hands Spyder wheels, which is the reason I bought it.
They butchered the back end.
I gave the kart to my friend, minus the wheels.
Can anyone ID the maker and year?
Thank you!

Another angle. It appears they cut the top tube from the axle and raised the rear with that drop down lower attachment