I have never seen under a MM, I assume the original does not have the big circuit board under the playfield but more in the backbox.

Yeah mate, an original MM has the standard 3 boards in the backbox and the underside only has a series of small boards to hold the lights for the inserts.

Here's an original I have for comparison. Sorry about the filth, this was an untouched as is pre-restoration photo.



Time will tell I guess as to whether it was a sensible decision to shift a majority of the backbox components and circuitry to the underside of the playfield - particularly right next to the troll solenoids which pop up and down regularly during the game.