The tanks are interchangeable as far as fitting them into the tub. There may be some additional fittings that will require a plug or two.
As far as the tank with the dent, as long as the metal is intact, it is still serviceable. Once installed, no one but you and everyone on this forum will know.
You could attempt to pull out the dent, but that could be a challenge.
The holes, if any, can be soldered up or better yet, a small piece of metal placed over the hole then sweat soldered. Just sure the tank is vapor free.
I would use the old tank, and destroy all the pictures of it.