Have you verified with TOW the barrel is actually in stock?
TOW shows a Green Mountain Drop-in Barrel for the .54 caliber T/C Hawken (1 inch flats) in their catalog, for "only" $219.
I sent TOW an email to confirm the price, and that it is still available.
"It has been out of stock for about 2 years."
(Shame TOW can't or won't update their catalog)
From my email conversations with Green Mountain, Green Mountain no longer makes the T/C Drop-In Barrels, for any caliber.
Whatever TOW (and other dealers) had in stock is/was it.
The 1:60 or 1:70 twist is "Ideal" for PRB. They might do O.K. with a short conical, (no promises or guarantees) but will do best with a PRB.
The longer sight radius should improve accuracy.
The extra barrel length should give a slight boost in velocity, using the same powder charge as in the shorter factory barrel.
With the proper load, a .490 PRB is "sufficient medicine" to take pretty much any big game animal in North America.
I know in Idaho, .50 caliber is the minimum for larger than white tail deer, mountain sheep and goats, and a few other critters, including black bear.
Obviously, you will have to sight in and work up the most accurate loads again, if you get a new barrel.