I would just pick which one you like better and bend the metal stop on the other.

Never seen a guide although if you measure some of other games hopefully you'd find a common number.

Sometimes if you take off the bracket you'll see holes where one was moved, or find the bracket is bent.

On gottliebs of this era a good assumption for the rest angle is "parallel to the inlane"

Except DAC doesn't have inlanes.

Trial and error for the setting, although you can use the settings shown in photos from other games of this type flipper arrangement as a go by. There should be enough DAC and PAC photos on line to compare to.

As for the difference in stop position, I have found the longer the distance between the coil and that L bracket, the more power it gives the flipper. In my book I make them the same, but do adjust that L bracket for power tweaking.

The end of the left flipper plunger's linkage looks pretty worn.
On the next order, I need to order a couple because the hole
the plunger's pin goes through is quite worn on the Flipper
Parade..

Correct. The lower bakelite link is mangled at both ends. Looks like the upper link may have been replaced with new at one time. Notice the distance each pivot arm rests from its respective metal stop. The difference in rotation between the two is obvious. Best fix: replace the lower link (PBR has the material) using the upper link as your pattern. Quick fix: move the upper stop bracket away (has the slots for this), or screw in a metal shim piece onto the face of the lower stop bracket.

This recent tool post (and thread) may be helpful in replacing flipper link roll pins. Can be a challenge:

https://pinside.com/pinball/forum/topic/gottlieb-flipper-rebuild-mid-70s#post-7381008

If you're buying a replacement link from PBR anyway, he also sells the correct size roll pin punch.

A pic of the playfield side with the flippers at rest would show that. But, aren't those 2" flipper positions adjustable via set screws on the flipper shaft? I can't recall.

I don't think there's really any set point, but I'd say the upper one (the right one
when the playfield's installed) looks about right, or when the flippers are at
rest, running them even with the metal guides just below them may be a good
start for a trial, but I wouldn't give them any more throw then that..
I'm guessing the right one is pretty close to where you'll want to be with it..

The screw on the top side only holds the flipper plastic in place. Flipper position is adjusted like any other flipper.

Almost every part of the system can impact travel - L bracket, fiber link, plunger, coil stop. I generally try to make sure the L bracket is in the original factory position (determined by the screw hole that is not slotted), and the bracket has close to a 90 degree bend. If you then rebuild the flippers with new parts, they should have equal travel. With old parts you just get what you get, and it might not be even.