I have just started my research into this. Some years ago my SUVCW Camp wrote a letter to the cemetery to an individual they called "To whom it may concern". Apparently nobody was concerned because they never got a reply. I became a little more aggressive and addressed my letter to the Bishop of the Springfield Diocese. I found his name and title etc. so that the letter was a bit more personal. His office forwarded it to the superintendent of the Catholic Cemeteries in the diocese. I explained about the SUVCW being the heirs to the G.A.R. He replied saying that he was glad to know who it belonged to and that they never had any plans to sell it.
During my last visit one of the clerks in the office said that they had been approached on several occasions to sell it to the guy in PA that has been buying up cannon for a private collector.
The clerk was also under the impression that the city of Springfield had given them the mortar. I did not argue, but you can see by the plaque that it came from E.K Wilcox Post 16. I am going to try to find the post records. I have a friend that knows where most of them are for MA. (He wrote a book about them)
Thanks for your quick replies and good luck in Washington.

Steve T