bigger sprocket on a cat

#1
i believe i have a cat 250 frame and was wanting to put a 66 tooth sprocket on the back. has anyone put a bigger sprocket on a cat frame without having to cut the frame to make room for the chain?
 
#3
no its not the original wheel , the sprocket looks old its has a circle design on it, i counted it right now and got 62 teeth . when it give it throttle offroad it take a little bit of time to get up, i have another bike with 6 :1 gearing and it feel like a beast compared to the cat
 
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