Got a couple of 19" monitors mounted last night. Went pretty fast since I had all the blocking strips prepared already.
Here is a set of blocking strips for a Pac/Ms Pac/SuperPac/Galaga style cabinet.
First 3/4 x 3/4 x 23-1/8"
Second 3/4 x 3/4 x 23-1/8" plus 3/4 x 2 x 23-1/8" (this is the L-shaped blocking strip)
Third 1-1/2 x 3-1/2 x 23-1/8"
First strip (3/4 x 3/4 x 23-1/8") screws onto the baffle at the very bottom of the monitor area.
I usually lay the cabinet on the front for this next step. I position the monitor so it rests on the first blocking strip and the baffle between the CP and monitor areas. If you have the right monitor, it should balance nicely on there with out help. I then position the top edge of the monitor, and screw in the second blocking strip (L-shaped with metal brackets).
I use 3/4" hex head screws. They normally don't poke through to the other side of the cabinet. 1/2" hex screws will work, as will the original coarse-thread 3/4" screws from the cabinet.
Finally, the rear blocking strip (2x4) goes on, making sure it does not block access to the AC and VGA inputs.
I then stand the cabinet upright, center the monitor in the cab, and install the side blocking strips to keep it from shifting.
Here is a rear view of the mounted monitor.