The plum color is indicative of a Bavarian refinish on the trigger housing, bluing parkerized metal turned it plumb color. To find an Underwood barrel with the correct date range of the receiver will be big $$$$ and if you are going that far then you would also need to replace the trigger housing unless other parts indicate it was a Bavarian return. Was the cracked gas piston that when when you purchased it? I am guessing and I think you feel you have an Underwood that was "corrected" with parts. Did you see indication of a removed import mark on the barrel? The Underwood barrels I have seen are all machined with concentric circles which would make removing an import mark very obvious IMO. The U.S. Caliber .30 Carbines - Barrel Manufacturers