The visors.... I hope whoever installed the head liner inserted the mount screws in each hole a few turns before the liner went in.
If they did you should be able to feel around the area for the heads, make a tiny slit/ hole to pop the screw heads through.
If no screw heads are present find the aprox 1/2" hole the tension spring for the visor arm fits into.
Hold that arm up in the correct position and use a pencil ect to make a tiny mark at each of the 3 hole positions. A very small slit to fit the spring through. You should be able to use your finger tip to locate each of the 3 screw holes .A small sharp awl to make the hole in the liner.
Not sure what year of Polara you have. If the visors clip into the mirror base swing them to the center, clip both visors in hold the mirror up on the header use a light pencil mark to fix a position. Feel around forward and back for the mounting holes.
Good luck, I hope the head liner was installed by someone that put all those screws in before the liner went up.