I am starting to put together top and bottom. There is a very weak point in the Playboy Playfield: it is the post located right to the side of the Special/Extra Ball switch. That post is submitted to the Pop-bumpers on one side and from direct hits from the bottom of the playfield.
As you can see, the original hole has been enlarged by the repetitive impacts of the ball. The original mounting is done using a wood screw post, by Bally. Of course, after a few thousands of plays, this post gets dislodged and the wood breaks causing the post to float and break the plastic above. To remedy that weakness, I decided to mount instead a machine screw post, which is a lot sturdier.
All you have to do is extend the existing hole by drilling from the top, with a 4 mm bit.
The T-Nut is inserted gently and secured by the traditional wood screw:
The Switch bulb/socket is then placed back to its original position and voila... It is a little bit tight, but everything fits perfectly:
From the top, all is good and sturdy now: