Normally for that approach, there should be a 30 amp AC shore power and a 30 amp AC generator breaker in the panel. Only one of them should be ON at a time or you may have fireworks. Normally, there is a mechanical safety linkage between the 2 CB's that prevent both being on a once. Sometimes it is a see-saw like linkage; other times it is a slide bar. This was one of the ways they did things in the days before fancy ATS devices. I know, in this day of camara phones that have digital pulse tones it is hard to think in terms of rotary dial phones. That however, is the era your rig was born in.
Opp's now that I dig a little deeper, some PD models (like yours) had a shore power/generator selection relay in the AC/DC/Converter unit: http://www.progressivedyn.com/servic...l%20710778.pdf
). That is an early form of an ATS.
Troubleshooting: pdf page 12
Picture Layout: pdf page 19
Operators Manual: http://www.progressivedyn.com/servic...0%20Manual.pdf
There normally is a seperate 20 amp AC breaker for the other (rear) AC.