I miss living in SoCal for that exact reason.

You might have to send it off to a shop like Bill Bune.  And then order a new piston and rings from Enduronut when they tell you what size you need.

Your Dad might have put a few miles on that bike but looks like he took good care of it.

Got my DT3 cylinder back from Bill Bune a couple of weeks ago, quick turnaround,  it cleaned up with a first oversize from Enduronut.  

Glad i read this post.
I have recently come across such markings on two engines. My CT1B cylinder and another CT1 engine i picked up that was supposedly seized and was no such thing ( try refitting the idler gear correctly )
and yes i tried to understand the correlation between the two . Never seen that on any of the others i've stripped . Nice one Mark T.

Nice std rings came today. I can't seem to find the keep that stays the top ring? What am I doing wrong?? 

Not sure what your saying but if you mean the ring pegs they should be there close to the position the rings are sitting at now. If you squeeze the rings & turn them in the grooves then they should find the locating pegs. Unlikely to be missing. Ring expanders could cover the second ring peg "if fitted" but top L shape ring won't have one--in hindsight i doubt the second one would have an expander either in this model.

Yeah the pin. It had spring expander on the bottom when I tool it apart. I can see the pin on the bottom groove, not on the top groove

Should be about where the letter R is in your pic--i think. Move ring around that much & squeeze ring into the groove about there. Hope its there.

Found it!
helped to clean away the carbon 

If there's carbon in the grooves a broken hacksaw blade works so the square broken end can get right up to the peg. Just be very careful fitting the cylinder on over the rings. Could lay the bike on its side totally flat so the cylinder long studs will support it so gravity won't try to take over because rings need to be held in place over the pegs & squeezed at that point & very little room for error.

Simple green and soft toothbrush worked pretty good...