Just a mention that all frozen engines need not be "Frozen"! I was given an Elfin 2.49 diesel (the second Elfin that I got hold of recently. Not a lot of the usual things worked, but I eventually got the piston out with a wooden drift!
I cleaned everything up and oiled the piston and slid it into the liner. The piston top got as far as the exhaust ports (360 degree radial ports in the parlance of the day), it then stuck solid! The liner must have been distorted in a crash and there isn't much meat in the pillars separating the radial ports!
I am now considering if I can hone the bore out oversize and make a new piston. I am a sucker for basket case engines!
Andrew.