Section 7.2.2 Inventing Gadgets
Whenever you want to bring a card into play that has the Gadget keyword, you need a Mad Scientist to successfully invent it. Gadgets are usually goods cards, although a handful of dude and deed Gadgets also exist. Any card effect that uses the term “invent” (or similar) is referring to the process of bringing a gadget into play.
As a Noon play, your Mad Scientist can try to invent a Gadget you hold in your play hand; it's just like shoppin’, but not a sure deal. When using an ability to bring a card into play, that card can be a Gadget, but you'll still need to have a Mad Scientist invent it (e.g. if you use a card such as General Store or William Specks to play a Gadget at a reduced ghost rock cost, you still have to pay the cost of inventing it). The cost of inventing a Gadget is as follows: 1) Boot your Mad Scientist, 2) Pay the Gadget’s ghost rock cost, 3) Then perform a skill test using the dude’s Mad Scientist skill rating. If the resulting skill check equals or exceeds the Gadget’s difficulty, the invention was a success and the Gadget enters play. Attach it to the Mad Scientist unless the Gadget says otherwise. If the skill test fails, the Gadget is placed in your discard pile.
Gadget dudes enter play at the location of the inventing Mad Scientist unless instructed otherwise, but unlike goods they do not attach to the Mad Scientist. Once in play, they are treated like any other dude. Gadget deeds enter play like any other deed, using the normal deed placement rules.
As bringing in Gadgets is a Noon play, only the Post-A-Tron card text is what allows it to be a Dude in a starting posse.
Additionally, starting posse is revealed simultaneously and there is no mad scientist already in play to invent the Dude.
Unfortunately this is a leftover from the AEG era in which it was not fully clarified.