If you have allready removed the piston from the sleve you may need a new ring. If I remember correctly they had a Dykes ring which did not like being streached after being bedded in. The ring will need to be compressed so that it will fit back in the cylinder. To remove the piston and rod assy you remove the cylinder and then have to get the rod to slide right back on the gudgon pin in the piston. With the age and length of time sitting it is likely that it is gummed up.

Cheers