I've removed freeze plugs many times by driving a sharpened punch (square-ended chisel) through the center of the old plug, piercing it, and then using it (or a small pry bar) to pry or "pop" it out. I've never had one fail to pop out and never done any damage this way.

Please note: I'm telling you how I've done it. I have no knowledge of your skill level or tool quality, so cannot be sure that you'd be successful.

It seems to me you want the heater in the lowest plug -- heat rises, so you want to encourage the circulation through the coolong system. Is the right rear plug the lowest on the block?