"Inverter" or "Converter"? I'm not aware that the factory installed solar pre-wire that early, ane even if so, the consensus on the Forums is that the factory pre-wire is pretty light duty, and not up to handling a significant-sized solar panel array. It could easily be true that the factory installed a 50 amp converter, used when "on grid" or on "shore power" to charge batteries and run the 12 volt
systems, which at 12 volts would be 600 watts ...
For the solar side of things, you will probably be best off starting from scratch unless it already has solar panels on the roof installed by the PO, a good charge controller, adequate wiring, a decent battery bank, etc.
And IF you have the original factory Univolt converter, it probably ought to be one of the first things to go in your "upgrade" plan. The ones from that vintage are single stage and would in all events probably cook your batteries to death if you ever were "on grid" for very long.
Congratulations and welcome to the Forums. You will get lots of advice here, all free, some of it worh something, some of it worth what you pay. There are lots of threads on solar installs, so do use the search function and do some reading. Some folks on here will tell you that you can't run your coach on solar panels. Well, despite the naysayers, many of us do run on solar, but you have to have some sun, and you have to take into account, the limitations of such systems.
My smaller coach spends most of it's time "off grid" or "boondocking" and I have not used my genset since installing a photovoltaic system (equipment supplied by AM Solar) and a larger battery bank. But my coach is smaller than yours, I run everything from 12 volt
, and don't use an inverter (except for a couple of low-draw battery chargers that I occasionally run from a 300 watt inverter), have converted every fixture to LED lighting, and try to find cool sunny places to park the trailer. You can do it, but of course there are limitations. A good start is to go to the AM Solar website and read all of their "educational" materials. You'll likely learn a lot.
Keep reading, and good luck in your quest!