There is quite a bit of information on replacing Univolt systems in these threads but finding it concisely presented is another thing.
I am not familiar with solar systems (I still think pluto is a planet, for example), but I have recently replaced a Univolt in a 1965
Globetrotter and so I think I may be able to help a bit.
I'm going to assume you know how to mount the panels and run wires and such from you system and what you have coming out of that system is a positive + and a negative - wire that need to integrate with the AS.
The old univolts convert the 110v from shore power to the 12v
needed to power the three (or more) 12v
circuits. These circuits power some of the lights, the furnace fan, the water pump and ceiling fans. The univolt also charges the AS battery(ies) so you can still have these fixtures while disconnected from shore power.
My understanding is that the Univolts varied somewhat and that earlier ones in the 1960's had a univolt and a separate distribution/fuse panel. Later ones, perhaps yours since its a 70, will have a distribution panel inside the univolt. Look at this thread and it's probably what you have.
Now... Is your Univolt working? That is, is it both running the 12v
systems when you are attached to shore power AND charging the battery? If it is working and doing both of these tasks you may not need to replace the univolt at all. If this is the case, I'm probably at the end of my help to you. I'm sure it would just involve running a wire (properly fused/breakerd) from the solar to the univolt but I'm not sure exactly how).
IF your univolt is NOT working or you just want a more reliable charging source, then there are several models of converters out there. I went with the progressive dynamics
others use the Powermax Boondocker
Powermax Boondocker Converters
So if you get one of these converters, you now need a separate fuse box to deliver power from the converter/battery/solar panels to the 12v circuits. Here is a fusebox that will do the trick.
12V RV Fuse Box
The key thing to remember when installing this box is that the three DC positive inputs on the fuse panel don't care what the source is coming in, so this is where you connect your battery, your converter and your solar panel.
I am attaching a revised version of a diagram for this fusebox. I think it illustrates what goes where a bit better.
I'm sure I've missed something but hopefully others will chime in and clarify.