You only need room between the right side seat support and the third bearing support for the chain to run through. Assuming the seat tube, the one running from frame rail to frame rail, doesn’t angle back too much.
Send a photo of the right rear of the kart, looking forward.
206’s will fit nicely on just about any kart. Worst case, cut the right side seat support off and use a bolt one. That’s how Margay does their Ignites. It works fine.
Bob, it does appear you’d have issues with the seat tube. It appears to angle back and connect to the inner frame rail almost where the front of the third bearing hanger is welded on. That would limit the size of the rear sprocket you could use. We run anywhere from a 56-62 tooth gears, and I doubt you could get a 56 or 57 in there. If you know somebody with some 35 gears, see what might fit without hitting the seat tube. It does appear you have enough room for the chain to run between the right side set support and the third rail. But that would be pretty close too.
To make the chassis work by moving the seat tube forward might not be worth the risk of totally screwing up the chassis.
I might suggest taking it to an event where there are some 206’s running and see what might fit, where.
Sorry I couldn’t be more help. You might try asking on Bob’s 4 Cycle Forum, there’s a bunch of folks there with more experience then me.
We have two AX8/9 that we have run Clone, World Formula and LO206 on. Because of Arrow’s double leg seat mounts there was interference when mounting the four-strokes. I removed the stock mounts being careful to not cut or grind into the chassis tubing. Spot painted the chassis with Yamaha motorcycle touch-up paint and installed an aftermarket seat strut from the rear cross member to the seat. They work fine. I will say we run 219 gear as that is what the WF comes with and we have not had any gear clearance issues.