I'm sure I saw the same gun ca. 1980's. The piece is interesting for a couple of reasons. It appears to be mounted for display on an original Navy wrought-iron Marsilly carriage. It is one of a pair in Sta Monica, 10 inch Rodmans sleeved to 8-inch via a tube inserted in the muzzle, the "3rd. series" of conversions.
These are, per "The Big Guns" by Olmstead et al:
No. 47, insp RB, fdry no. 262 yr 1885, wt. 15980, Seyfurt, McManus, Orig ID: No. 102, MS, 1864 wt. 15176 l
No. 48, insp RB, fdry no. 263, yr 1886, wt. 16020, " " ", Orig ID: No. 103, MS, 1864, 15176 lbs.