As you know these worked by picking up power from the underside of
a suspension mount third rail, that was commonly safety covered with boards, or occassionally ceramic material, on top aand outboard side of the third rail.
They had spring and/or electro-hydraulic (some locos) units that maintained upward pressure on the underside of the third rail to insure good electric power transmission to the traction motors.
Modelling this function in any scale, much less a small one like 'HO',
with miniatures of the prototype- will prove frustrating and frought
with continuous broken parts and lousy power continuity.
Outside pickup units employed with two rail AC model railroads
( and by John Armstrong and Frank Ellison on their home railroads)
are not scale sized or representative in appearance of prototype
pickups. Now dummies have been made, but I believe they came with
Baldwin electric traction power truck side frames in 'O' scale. I would
guess that some one made dummies for other scales as well, in order
to enhance apperances.
Don't the many New York Subway 'R' class
models currently being made in 'HO' and 'O' have dummy third rail
pickups on their trucks? I know the prototypes rest on top of the
third rail in this caser, but doctoring them a little to resemble
NYC/NH pickups is not a big deal.
Good-Luck, PJB