In the future, if you do a wet comp test, put the cylinder at tdc, engine tilted so it doesn't pass through intake/ex ports and add some oil not too muck. Turn it over w/p plug, then add a touch more. Comp it and if your compression comes up then rings will help. That's the low tech method. You need each to be within 5%. If you were trying to sell that and the buyer showed up with a comp gauge at 125 psi in one hole over the others @ 130 it's game over.
I knew the piston was trashed when you found a piece of the ring.
Now, go buy a motor that has an electrical issue etc, take comp gauge with you or take a chance. Don't pay more than $200 and get yourself a head.
Here is an example of what I just bought: Engine runs but won't idle. Marina rebuilt carbs, I'm tired of spending money.
Fuel pump was bad $15 fixed it.
Next one: 2 guys comped it on a rope and said 115 psi was low. Yup. Fixed the choke wire it ran
Next one: Not sure how it starts...put gas in and turn key.
Age of the motor not important. How it was used/ maintained is.
Go buy a complete motor with some extra spares.