huntermn,
Even though SKB is correct,if you want to use the 375 barrel badly enough, you can do it. You will have to turn the old threads off and thread the shank for something convienent like 7/8-14.Then make a bushing to fit the new thread.With the barrel between centers, thread the bushing to fit the action. Other considerations:The barrels also have different "breeching", so you should measure everything to insure you have enough shank to fit to the action.I would make the bushing first, then thread the barrel to fit tight enough that a pipe wrench would be needed to turn it on, and use locktite on it.A little finesse will be needed to get the barrel to turn up plumb.
Mike