I think your question is ” How do I tell if I have a modded engine?” correct?
Check your bore size, CR80 1986-2002 47.00 mm, CR85 2003-2007 47.50mm, any other bore size is not stock. You mentioned 101, check you bore, if it measures 52.00mm, it is an aftermarket 101 big bore kit. Check your rules, might still be legal. Another thing to look for is enlarged transfer ports, these are the 2 little holes in the reed cavity in the cylinder you see when you remove the reed cage. In stock form they are rather small, look like a reverse capital “D”, 7mm dia rod fits snug, quite frequently they are enlarged. Also if your head has “O” rings rather than a gasket, it has been modified. Check your rules as what is termed “stock”.