Ok the engine swing arm is steel so that is good. The rear springs you can reuse along with the rearend being it is gas. If you have both clutches even better. You can also reuse the gas pedal, brake pedal and cables, steering wheel, steering column, steering box, front spindles and hubs, lower control arms and spring. Starter generator and electrical system. If you can find some one around you to tig weld aluminum you could cut the frame under the floor pan and lengthen the frame. Also have them reangle the column, the pedals should work as is.
Should you not find anyone who can tig aluminum, you will have to replicate the frame using steel. Then just transfer all the parts from your frame over. The good thing about all this work is you will have FNR.
You could also say screw it and just replace the engine in the kart and ride it like that. Could you take some good pictures of under the seat where the engine is or was so I can see what you have exactly to work with. No matter what you decide you could end up with a really nice creation. Although I would probably upgrade to a 420 or the new 445 engine because I think the 212 will be too small. Stock the golf kart had a little over 8 hp. And we’re kind of sluggish.