250-500cc Wr 250 to 360 swap

Hey all, I have a 1999 Husky wr 250 that no longer runs. So I decided to open it to find the cause. The cylinder and piston have deep scratches. So I ordered a new piston and the cylinder was to be sleeved. The piston came now and unfortunately didn't fit. That's because I just now find out that my engine is not the original '99 but an early '91 cagiva WMX 250. So the new piston is aprox. 66.7 bore, while the old piston is aprox 69.9. The distance between the pin and the head of the piston is also different so that i can't use the new piston even if i sleeve the cylinder to its bore size.

I was thinking to buy a late model rod, maybe this way i will keep my 250cc, I will use the new piston that I bought and I will just sleeve the cylinder. So what do you guys think I should do? Remember that I don't want to spend any money on another piston kit.
Oh, I have the opportunity to buy a WR 360 used top end. Will that fit or i'll have to change the crank also?

I don't believe the 360 top end would bolt to that. I could be wrong. But I would think the issues would be the crank (360 is longer stroke), 360 jug size (the piston is massive, so is the cylinder), powervalve (not sure if your 250 has the same powervalve action as the 360s have). If it was able to actually bolt to the cases, then I would think there would be a significant amount of machining required, and it would cost much much more than a new piston kit.

Good thing is, you if you can't return the piston kit, you should be able to recoup some of the cost by selling it on here.

I believe that the conrod from my early model engine (cagiva wmx), is longer then the later model of Husky wr 250. Otherwise I don't understant the difference between my piston and the newer piston, why is mine 69mm bore? From outside the engine is identical.