How long did the mounting and "stand offs" continue for?
We recently (about 2 weeks ago) brought in another male to try to socialize/be friends with our existing male ... and each time we put them together, the older male goes right for the mounting ... followed by stand-off gurgling and even some teeth chatter. No blood letting or anything ... but it's hard to watch all of this other stuff happen and not think that the new/slightly smaller pig isn't feeling tortured by all of this.
Any thoughts?
Well it depends on the pigs and the situation. For me, there was no mounting during the intros, just a little butt chasing and all. The mounting started once they were in the same cage.
You said "Each time we put them together" Does that mean that you have been separating them? If you are make sure not to any more, because if you separate them during intros, the next time they will just have to start all over again with finding out who is boss. You just need to intro them once for about 1 hour give or take some, and as long as there is no blood shed, they can be put right into a very clean cage together, so that there are no smells of either pig.
All the mounting and such that you are talking about is totally normal. It's just the one pig making sure the other knows that he is the boss. Your smaller pig will be totally fine.

Just make sure that nothing turns into blood shed.
My Phoenix was the same way when I introduced Fus. Phoenix used to be the top female, but the Fus took her place. Whenever Fus would mount or chase her, she would scream out as if she was being hurt, but I knew she was fine and checked her for bite marks and such every day, after a while, and after Fus made sure everyone know she was boss, Phoenix and her are now the best of friends, and have no problems being together. Also make sure to weigh your pigs more often once you have them in the same cage, and that you have double of everything for the added pig. This is because some pigs will guard food and such, not letting the other one eat, weighing helps you to make sure that no one is losing weight from not being able to eat.
And last but not least, a big cage also helps a TON it makes sure that each pig has a chance to get away from the other, and chill out without having to be near them.
Hope this helps! (Sorry for the long speech xD)