Tricky both in access and installation.
You have to remove the two screws on top that hold the "N O P" (or what sign is on yours), then under the playfield, 4 screws, a few cable clamps and a molex and the assembly pulls out the bottom.
Once out you have to take off one clip that holds the rod that hold the 3 targets. You can pull it out half way or and leave the targets dangling on their return springs.
Then you can remove the optic.
Here is the tricky part, the marking on the old and new have not specific orientation on them. The Original ones had writing on one side, new ones have an E+ and S+ on the caps but that don't help and you have no board reference to tie that to.
Sooooooo, seeing the opto is no more than a lamp and a diode pair, I ohm'd the old one out and found the 'diode' side and did the same for the new one and matched orientation. Either I was a technical genius, or I just got lucky as it's a coin toss on the orientation.