I think you can find a short conical, like the Ballettes from Buffalo Bullets, or the LEE R.E.A.L. slug that can be shot from your existing barrel. That .54 RB weighs more than 1/2 oz. so don't be underestimating its ability to kill out to 100 yards. The short conicals may give you a slight advantage.
Moose don't have very many predators, naturally. Bears are about it. Sometimes wolf packs.And a high stepping moose can usually out run even a bear in the kind of terrain where they live. The bears tend to only get the old, sick, and lame moose, injured some other way.
The point is that Moose are not particularly wary animals, and they don't bolt at the first sight of man. I agree with BrownBear. Work on your stalking skills, and on your ability to accurately estimate range over rough ground. Buy a short range rangefinder, and use it. If you use a guide, most likely he will have one. Practice moving bent at the waist to reduce your outline as you near game.Practice move around brush, and not over it. Moose have good ears, and they also " Listen " to vibrations through the ground, with their large soft padded feet. Learn to move when their heads are down, and stop dead when that head comes up. It should not be very difficult to close to within 50 yards, if you simply practice your stalking skills. Listen to other forest animals for alarm calls as you move. They tell you when you are moving too fast, or making too much noise.
If archers can get close enough to take moose with a bow and arrow, you should have no trouble getting within range to take them with your .54. Save the money on the new barrel, and use what you have. Spend the time this summer practicing your stalking skills, instead of trying to find a new load and bullet to use on what may be a once in a lifetime hunt. Shooting you current load will serve you much better.