Smoke units for 3rd rail are pretty easy. I JB-Weld a spring to the bottom, and solder a brass extension to the screw-in funnel for a standard MTH steam smoke unit. I remove the resistors and put in a single 20 ohm resistor closest to the stack exhaust.
This scheme allows you to remove the smoke unit easily for maintenance, and you know that will be needed in the future. I reach down the stack and unscrew the brass extension first, then just compress the spring and drag the smoke unit out.
For the tether, I either try to line up some holes in the MTH 10-pin connector PCB with the original 2mm holes, or drill and tap my own holes if theirs aren't in the right place. A stack of Styrene on either to support the PCB and I'm all set. You will normally have to enlarge the hole in the boiler shell for the MTH connector.
