I'm not really up to speed on PreW AF. (or post war) But most basics about trains carry across brand, scales, and era imo
Wouldn't it be possible for the 4r car to work off the center if a new shoe was made or adapted to run on the center? Run on a ZW, it may need the Lionel whistle relay, that's about it. (doesn't 4r inside rails just deliver whistle power from a plain old button switch? So they didn't have to pay use fee to Ives or Lionel etc?)
And the 3r car; a possible example of a mod adding a whistle rather than a repaint?(different mount). If ran on GarGraves or other track with all rails isolated, no telling what a former owner had rigged.
Since you have a ZW, that whistle signal needs a shunt coil relay that only pulls on DC, not AC. 1 AC cycle, has two waves, one ± one - . The ZW knocks off a little of one wave. The remaining imbalance an "offset". An offset can be measured as a dc+ or dc- wave (a pulsed dc vs the constant form we think of from batteries) So from what I gather here, the AFs need the center shoe and Lionel relay to run off the ZW and whistle like a Lionel would. Not hard at all imo.
Some folk are more concerned with operations than originality. Fine by me. I just think it could be a very reversible mod and still achieve an operation goal. I'm the type to save the old parts in a ziplock with a note while "trying to stuff a big block into anything that rolls"
Brass automotive feeler gauges make a nice flexible shoe with good contact and are found easily and cheap when worn out. A set has a few usable thicknesses, but ask, there may be singles under the counter at some places. (ACE/ACO has them sometimes too)... Mechanics with a big set can replace just one bad blade that way.
