Ross,
Post a pic. Clyinders can be made like new with a replate, but unless the plating is flaking, deeply scored to the aluminum, or worn very bad its probably not neccessary. Nikasil is very hard stuff. These are fixed with replating and diamond honing to size, no overboring. Even damage to the aluminum like gouges can be fixed by welding before replating so a two stroke cyl rarely needs to be replaced. As far as measurements, unless you have an accurate bore mic or take it to a shop that does, don't waste your time, the errors introduced can be greater than what you are trying to determine. Likely you can clean things up and go with a Vertex a size or two up from your cyl. size. If its making noise thats bad as the shirt fatigues and eventually cracks. Thats why you change pistons even if they appear in good shape.
I'm pretty sure a 66.33mm is an "A" size Vertex. Wiseco only used two sizes. Is your cylinder stamped "A" near the rear base?
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