As the title states the sights and barrel band swivel appear to be a few degrees off TDC and BDC.
I didn't notice this until I mounted a scope and put a level across the rear sight. While I realize that placing a level on the rear sight may not be an accurate way to check, it did make me look closer at the sights.When viewed from the muzzle the sights appear to be slightly but noticeably towards the 1:00 position and the swivel slightly towards 7:00.
When I pulled the barreled action from the stock there are witness marks that are aligned.
The rifle is an FN action (J.C.Higgins)that has been re-barreled to 9.3x63 with a Lothar Walther #720 barrel and NECG barrel band front sight, NECG rear sight, and barrel band swivel.

Any advice on how to go about getting this corrected would be appreciated.

There is always the possibility that the metal is not bedded squarely (ie: canted)in the stock as well.
Take the rifle apart, use the flats on the bottom of the action as a quick reference to set level with a quality level. If you can do this in a vise that is backed by a surface that is also level with the action after setting it you can stand a square on the flat surface and line it up with the sights and swivel centers (or not if they are out of square). I'm sure a gunsmith with quality equipment has a better way but this will get you started.

If the barrel is in fact not aligned with the receiver, the barrel can be pulled "timed" correctly by trimming an appropriate amount from the barrel's shoulder and headspace reset. Standard gunsmith work.