Oh boy. You do have some work ahead of you.
From about 1960
Airstream was still trying to figure out how to handle sewage. Prior to that time trailers didn't have black tanks. The toilet either flushed to a sewer connection or a "gopher hole".
Our first Airstream was a 1960
Pacer. It used a modified brass wedge gate valve for the dump valve and the dump port was plain old Schedule 40 galvanized pipe--no locking pins on the outside.
Since it was just round pipe I found that I could bore out the inside of a modern plastic dump valve adapter for a slip fit on the outside of the pipe, fastening it in place with stainless steel machine screws tapped into the pipe and the whole thing sealed with pipe dope. That worked "OK" as long as we owned the trailer.
That option doesn't seem to be available since you have bayonet locking lugs cast into the outside of your dump port. Vintage Trailer Supply has some advice and conversion components
Waste Valve Adapter for Early 1960s Airstreams
Thetford Valves & Fittings
Here's another reference on replacing everything back to the tank:
Brass Thetford Dump Valves - Vintage Airstream
You're looking at quite a job, but it's worth it, as the old dump system wasn't big enough and the RV industry has learned a lot since it was made.
On the plus side, having done the job, you will be eligible for membership in the exclusive Royal Order of the Black Tank--an organization few have any interest in joining. . .