Imo, using a commercial "router jig" with a mill is counterproductive. You do not need it. It is a lot like new shooters wanting to go to a 25lb, light recoil, light trigger prs rifle- it does not allow/require you to learn the fundamentals and build you abilities.
Buying more mill specific tooling (and learning how to use it) will get you further down the road to greater capabilities than buying a jig.
If you do not have a blueprint yet, google one off the net and stare at it a while.
If you are new to machining you might consider downloading Ray Brandes (ray-vin) excellent tutorial. He goes as far as breaking down the coordinates that you need to machine your pockets to and gives you his fixtures blueprints that he uses on a 0%.
For an 80% you do not have to make it as complicated a setup as he does simply indicate the "deck" of the reciever flat as the reciever is set in the vise between 2 1-2-3 blocks like so ( safety stops above the block):
Now find the centerline of the reciever above the 1-2-3 blocks with an edgefinder (measure width of blank, edge find, zero dial/dro, move in 1/2 the width after accounting for your edgefinder radius)
Now you have a y axis zero. Next find the x axis zero relative to a gauge pin (or other approximately .250-.251 round thing you stick in the front pivot pin hole) by using a edgefinder as above (zero dial/dro once you find the edge and move in .125+radius of edgefinder from the front edge of pin you are locating from, reset zero)
Once you have the x and y axis zeros you can "paint by numbers" using the info off of a blueprint or Brandes tutorial to make your pockets and trigger slot relative to the front pin.
Next flip the reciever on it's side, buffer tube and .750 radius portion of lower outside of the vise jaws and indicate it level in the vise( the deck and bottom of a 80% should already be parallel to each other). Short of using a cheater bar on a kurt vide you shouldn't damage the reciever. Now find the front pivot pin location . Methods vary from as ghetto as eyeballing a drill bit in a chuck, to using a DTI to indicate the hole (what I reccomend a begginer to practice), to using a tool makers button and edge finder , to using a co-axial indicator or any of the other ways a machinist could skin that cat....
Once front pivot pin is found zero x and y axis move over and drill and ream the trigger/safety/hammer holes per blueprint
Done, no jig needed, no need to worry about jig compatibility with your "billet 80" or buying another jig to do a ar308 lower or pcc lower or....