Chris , I believe that you only need the two screws. I don't know the size but I do know that they are small....like an #8/32 or #10/32 screw ( I am only using these sizes as a comparesion for approx size)...also these screws are very short so as not to protrude into the dist body . My workshop manusl shows the screws, but doesn't give the size.
I beleive that the screw that holds the electrical connector to the dist. body is the same size...I am not certain of this but I kinda recall that it is the same screw.
Check the dist. body to see if one of the screws still might be there. When you go to reinstall the advance, the little arm goes through a hole in the body and around the post on the plate where your pick-up coil is mounted to, replace the two screws and connect the vacuum line. You should be able to do this by only removing the dist. cap and not have to removethe clear dust cover under the cap.
If you do have to remove the dust cover you will have to remove the rotor....be very careful on this because I Went to change my rotor last tune-up, and the roter was stuck on the shaft. I pulled up on the rotor, which pulled up the shaft, which pulled the springs off of the centrifical advance weights.