On our 59 the charger actually goes under the bed next to the water heater. The line runs from curbside the front window up through the roof and back down in the back. It's VERY under rated by todays standards as is most of the 12v
system when the lenghts they run are taken into concideration. I would not add a inverter without some serious wire upgrades and I would keep the charging under 40 amps and place 40 amp breakers on both ends. The wire is only a 10 gage and much more power then that and it could be overheated.
As you can tell I been mulling over these problems.
When I redo Ours I May relocate the battery into a sealed box under the goucho. The chager will be next to it. I don't like the Charger and battery so far appart. To much room for damege to the cable. It would need to be 8 gage possibly 4 concidering the distance and load demands that a inverter would place on it.
Our battery box is also toast and I want to get the spare off the bumper and relocate to the tounge. That's still in the air as we are trying to keep the appearance as close to original as possible. Just a LOT of weight on the bumper the way Airstream did it. The main bracket is a peice of 3/16 C channel. The whole assembly with spare has got to be over 100lb. If I can lighten it up it might stay but I doubt it. Putting it on the A frame and going to aluminum rim and Radial I would move 60lb at most up front. Batteries would shift back some.
Moving this also frees up some weight concerns for a gray tank I plan to add just behind the axle.
There was not enough room to drop the battery into the A frame of the hitch behind the LP tanks like the newer units. I don't want to run those narrow batteries like the stock box excepts. I may also want to run a pair of batteries and by giving up center drawer of the goucho I can get all the gear and batteries in there By sinking them into the floor or raising the Goucho 3 inches and building a sealed box.
Your question is Not as simple as it sounds is it? LOTS of things to concider when dealing with a 40+ year old camper.
In your position I would concider opening up the center seam of the belly and install a 4 gage cable between the rear area where the original charger is located and the battery. That sounds like a lot of work but that will give you enough capacity to run a Inverter and run the bigger 60 amp chager that far from the battery. Don't forget to gromit all the holes so the cable doesn't get damage. Wear a respirator because the insulation in the floor is nasty.