I assess antiques for people and I have to look for signs of age. My guess is that the cast iron piece shown is a lot younger than 60 years. Don't have time to go into all the stuff I look for but part of it is the color of the oxidation on the item, generally red rust means something relatively new. If that item was as old as they think there would be a particular corrosion pattern on the top designs where rain water pooled in the dips; there isn't.
Here's a possible scenario: There was some kind of somewhat valuable cannon on the marble from 1940's thru 1990's. Someone took it, replacing it with this repro so "disappearance" would not be noticed. Many such things have happened.
In any case, I don't think the cannon pictured has much age. It has the fat, multiple rings that are the identifying characteristic of all the sizeable Chinese repros I've seen. Those items used to wholesale for $200. ea. by quantities of 20 or more, came collapsed in cardboard boxes with assembly hardware. If someone thinks that repro is older, that's fine, all I can do is give my own opinion.