I'd run that action and trigger assembly through a few cycles in an ultrasonic cleaner. It can work wonders, at times.

In case anyone is still wondering, the next to last pic posted confirms it’s the first version Miller.

Wow. That thing needs a good bath and a cleanup

You could get both triggers with either the rocker on the front of the trigger, or the selector on the safety while they were still a family operation. The selector on the safety was a little higher than the rocker selector. I had both put on Parkers in the 80's while they were still Miller.