Old-style 20GA barrel rim cut modification

[GreenLightGo]

I bought my 20 gauge Wingmaster used in 1986. The receiver serial # prefix is S, which according to various sites means it was made between 1968-73. The suffix X indicates it’s a full-size “heavy frame” (not LW). The full choke barrel that came with it has a star preceding the “20 GA.” and a BB date code stamped on the left side. I understand the star means the barrel was made after 1969, and the BB code means it was made in Jan 1981.

With that as background, here's the problem. I recently bought an older barrel (fitted with a Poly-Choke II) with an EWW date code and no star, which appears to mean it was made in Oct 1950. This barrel ring fits over the magazine tube, and the barrel seats fully in the receiver. But when it’s assembled, the breech bolt will not come all the way forward. It seems that either the breech bolt or the slide assembly is striking the rear rim of the chamber, which is noticeably thicker on the older, EWW-dated barrel. See the photo below, with the EWW barrel on the left. Comparing the 7 o’clock position of each barrel in the photo (as installed, it would be at about 10 o’clock), you can see the difference. From online research, it appears that in 1969 Remington changed the angle of the rim cut on the mouth of the chamber from 45 to 55 degrees (and therefore added the star marking on post-1969 barrels).

Here’s my question. Does anyone have experience with modifying the older chamber to allow it to fit with the later model bolt/slide assembly? To me, it doesn’t look to require a lot of machine work, but I’d appreciate your thoughts on the matter. In the alternative, would an older bolt/slide assembly work with my current fore-end and receiver, or could I modify my current breech bolt and slide assembly to work with the older EWW-dated barrel?

I know it would probably make sense just to buy another barrel with rem chokes (although non-LW 20GA 870 barrels are surprisingly hard to find and pricey) or even buy another gun. But as my first shotgun, this 870 has great sentimental value to me, and I’d like to use it more often and with more flexibility than with just the fixed full choke barrel.