My mid to late 1990's 220 came with a polymer hollow guide rod and a green spring. Should I upgrade to the carbon or SS rod? Are there any advantages to upgrading or just keep it the same? What can be done to improve accuracy on the 220?

I have a couple 220s with the polymer guide rod. I have replaced them only because I have had a polymer guide rod on another brand fail.

The solid guide rod will give you a little added weight to the muzzle. I do not think it has made any marked difference in performance.

As far as improving accuracy the best thing I can think of is to get a good trigger job and lots of practice. Then I would look to a good set of sights. After that here are some aftermarket match barrels that you could look at.

Good luck with a great pistol.