The damaged threads in the cylinder can be repaired with a helicoil, and this results in the threads being stronger as they are now hardened steel rather than aluminum.

The 666cc bore kit is 95mm, and requires the cylinder to be bored.  Does the $300 price include a bored cylinder?

If your cylinder is in good shape, you can get the stock 94mm size Wiseco piston and use it without the cost of a cylinder bore.  The difference in horsepower is likely very small......the change in engine size from 652 to 666 cc is only 2%.....if your engine is 30 HP with the 94mm the 95mm will bump it up to around 30.6 HP.  (NOTE:  The biggest HP bump comes from the higher compression.....and both the 94 and 95mm Wiseco will get you that increase).

I have bumped the listing for the 94mm Wiseco to the top of the Marketplace section.