Help I’m replacing a drain and plug in my tub

I have an enamel tub and the stopper for the drain has never worked, probably because it’s missing parts. At any rate, I decided that I would replace it with a tap drain. So I went out and bought the new drain and brought it home. I also bought this tool for removing old drains. However, my drain doesn’t have the “+” at the bottom. It only has two very small square nubs across from each other near the bottom of the drain and they only stick out from the side of the drain a few millimeters. So, this tool has long grooves in it for just this sort of task. I put the tool in the drain and used a large crescent wrench to twist the drain off but it won’t budge. I tried using a hammer but I’m afraid the tub will crack so I stopped. I’m no weakling either. How can I get that old drain out? Has anyone had a similar problem? Did liquid wrench work? Are there any tricks that I could try? What sort of chemical will break up that adhesive? Thanks for any help you can give me.