If the Herco is in good mechanical shape why not just upgrade the controls to a modern system. I have a very low tolerance for antique controls anyway.
As far as CAM software for either machine, just about any CAM software will work. Just requires a control specific post processor. Since you are already using Inventor, Inventor CAM would be an option, or you could use Fusion 360 which has CAM built in right out of the box, and is a lot cheaper than Inventor with nearly the same capabilities. You can import the Inventor files right into Fusion 360.
https://www.autodesk.com/products/in...b=subscription
https://www.autodesk.com/products/fu...b=subscription