I think it's worth a try at running it although I'd use a healthy dose of castor to be on the safe side. The ring will be stuck at the size of the bore so most of the expansion will be of the piston pushing the ring even harder against the liner, hence the use of castor. Any clearances around the ring will be full of old gummed castor and that's what needs to be softened and get some of it squeezed out by the expanding piston. I've had success at freeing a ring by squeezing very hard with a fingernail alongside the ring gap pressing the ring further into the ring groove. Once one end of the ring starts to move just a little then any solvent like acetone or fuel will begin to get drawn in to the ring groove by pressing and releasing and it'll work its way all around until the other end of the ring frees up.