Is the part number on top of the piston the same on both sides? And in the last picture it looks that you have sealant on your base gasket? And its kinda hard to tell but kinda looks like there might be 2 gaskets on it?
+18 is going to be all but useless with anything except something with 150+ hp... Id start looking to sell you bike and buy a BIG motor if your going to use that chassis! Post some pics of it!
You looking to sell that chassis? Ive got a complete triple motor/pipes/carbs/ign that would go really well in that big of a bike. But Id also entertain buying the chassis from you!