It is a mechanical brake. There should be a plate welded to the frame that it will bolt up to. I can get a picture of the brake caliper itself this sat. Let me know if this helps.
Thanks. My neighbor asked me, I just laughed an said I have no clue. He's pretty excited about it. 1st gokart ever. Looks pretty rough to me. Came with the original Robin engine. It's in rough shape.