Not sure if this has been addressed but a forum member asked to buy a couple sleeves from my 400 four. Took about 20 minutes( 5 to preheat and 15 at 350 deg.
Items needed: I used an old baking tray and four same size sockets. The dead blow hammer is to get the sleeves moving.
This is how I arranged the cylinder, elevated so heat could get all around it. Top of cylinder down. BTW, photo was taken after liners were removed.
Into the gas oven lower rack. Turned oven to preheat 350 deg. Once temperature came to 350 I timed 15 minutes, removed cylinder, tapped sleeve with the dead blow and the liners fell right out.