Drilling the Ball Guides
 

This is the hardest part, because stainless steel is tough!

Strip the playfield and remove the ball guides on either sides. The blue tape shows the nuts that you have to remove under the playfield to do this. There are two nuts under the clock motor control board as well. You have to remove the board, a great chance to clean it.
You'll also have to undo all of the connections that go though the top right hole. Plus all of the connections that go through the clock hole.

 

There are a couple of others that you will find later, they can be freed by reaching down behind the playfield.

Before you remove the guides, run a piece of masking tape across the channel so that the edge of the tape lines up with the hole. (Cliffy tipped me to that one, thanks!). This tape is your guide for drilling for the optos. Head off and do the ball guide holes now, if you like! I did.

 Tear the tape so that each guide has its own piece. Remove the guides for drilling.
   
Take the template and screw it to a flat piece of scrap with four of the #6 sheetmetal screws from the machine. You want to keep to the right, as you see here. Remove the template and screws from the wood, and drive the top two screws fully through the template.
Screw the template back into the wood with just the top screw, most of the way down. Insert a guide so that the edge of the tape aligns with the pilot hole. Put the bottom screws in, and tighten it down. Make sure that everything is aligned. Remember, you want a hole near the top and aligned with the magnet. Use a small drill to make a pilot hole. I used 1/8" and a drop of WD-40. You will be fighting a bit with the other end of the ball guide.
Once you have a dimple, you can take the guide out of the template. I drilled the first one all the way through. It turns out that a dimple is enough.
Next, I used a 17/64 drill to make my opto hole. I went a little bigger than 1/4" for test purposes. Again, a little WD-40 helps. Clean the rough edges of the hole by hand with a bigger drill when you are done. Repeat for the other guide. Here's why you have to be towards the right. There's a bracket that interferes with the scrap wood. 
Here's the first one installed in the machine. And the second, with a 1/4" Lucite bar through the holes. As you can see, the template makes this very easy.
Remove the opto brackets from the boards by unscrewing the #4 screws. Insert a drill through both holes - 3/16" is good - and put the opto on it for alignment. You want to be 1/* or ao away from the guide.  Drill a pilot, and insert the first screw.
Check alignment, drill the other pilot hole, and insert the second screw. No need to go tight yet.

Remove the screws and plastic when done.

Repeat for the other side. The ball guides are not parallel, the drill is your guide!
Reassemble the opto boards to the plastic. The dimples are on the board side. They accommodate the connector wires. Tighten the screws to snug, don't overdo it. You could put a drop of CA adhesive in the threads first, these won't need to be disassembled again. Put the optos in the machine. Don't tighten them down to much. Acrylic is strong but brute force will crack it.

Dress the wires as you like. The receiver wires run as shown.

And here are the transmitter opto and wires.

That's it for wiring, connect them up under the playfield and re-assemble the machine.

Last step. We're almost done with the template. Put it in a vise, score it with a saw and then whack it with your hand. It will break into to parts. the top part is scrap, we want the piece left in the vise, which is part of the magnet spacer.