Steven,
Yes, your two locos with the lever sticking out of the top of the boiler have the reverse unit in the boiler, and there will only be two wires to the tender, that plug into the fiber plate under the cab roof. The other engine has the reverse unit in the tender, and you'll see a similar lever protruding through the bottom of the tender. This lever is the "lockout" lever which disables the reverse unit--in whatever position it is in if the locomotive is "hot" if the power is off, it will lock it in the next position. That could be neutral (no motor runs) or forward or reverse. Unlocked, the drum will rotate 1/8 of a turn each time you turn on the power--if the locomotive is right side up! It relies on gravity to return the lift lever that rotates the drum.
I don't know how much more toy train stuff this forum will tolerate, so feel free to email me.
S'
David D.
BTW, with these reverse units, your metal engines are likely '46 to '52, and the plastic one should be about '53 to '56. If the plastic one has a smoke unit, you have to unscrew the red plastic stack inside the smoke stack before you take off the body, or you'll break it off (don't ask me how I know this!). Earlier units with smoke in the boiler, reverse in the tender, had a brass stack and they don't break, but you still have to unscrew them!