No, I don't believe you have a "120 amp system". The original Airstream of that era had a 30 amp, 120 volt system. The largest RV systems even today are a 50 amp 120 volt system (actually two legs at 50 amps each, both 120 volts).
While a 50 amp, 120 volt system probably has barely enough capacity to run your trailer as an all electric unit, if you manage your use carefully, not all campgrounds have 50 amp outlets. If you are in one with only 30 amp service (real common) you will not have enough capacity.
Why the desire not to use propane? It works well, is very proven, allows you to dry camp (boondock) easily, and without it, you will make your Airstream very hard to sell.
You need to look very carefully at your plans for an all electric unit, and learn a lot more about how much power each device takes vs. the capacity of your system. I think (and hope) it will change your mind.