Good compresion is just one indicator of engine condition now you need to visually inspect the piston skirts. Pull the carbs and inspect through the intakes, slowly turn the engine over so you can see all the skirts. Repeat on exhaust side, you'll probably need to pull exhaust y pipe.
Polaris twins are suprising if it looks good .. run it. The triples usually show cracks at 3000 miles. If you find cracks obviously replace the pistons and have the bore checked. The other things you want to check on the machine is chain tension in the chain case and oil level if not change it. Also clutch maintenace and chassis lubrication. If you want to get into it e-mail me and I'll give you some more info.