Does anyone have a technique to get the piston out? Preferably while doing
the least amount of damage. (So no explosives, please!)

Take an old spark plug and break out the ceramic center, then thread the
steel body for a zerk fitting. *Be sure both valves are closed, hook up
grease gun and start pumping; you might be able to build enough pressure
(grease guns are cabable of several thousand psi) to break the ring and
force the piston out or even push the liner out of the one-piece
cylinder/head.

Adding to that idea heat the whole thing in an oven and then pack the
bore with ice upon removal. Remove the piston and the steel liner as
one assembly. Then renew as one would normally with a Franklin
cylinder/head combo ????

Never had this problem, and never tried this fix .............. Pure
speculation on my part.
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Leon McAtee
Will remember not to do the same with my Franklin :-)