"Visible" F-units with plexiglass panels

Last year Railroad & Railfan magazine had an article on E-units where in a sidebar they mentioned a group of "visible F's"- F3 and F7 B-units that were equipped with plexiglass sides and specially-painted interiour piping and were used to educate railroad personnell. However, other than saying that 4 F3B's and 1 F7B were used, it gave no details. Examining available evidence makes the conjecture that two of the F3B's became Santa Fe's 32A (2nd) and Monon's 64C (2nd), but nothing comes to mind regarding the other two. Anybody know anything for sure?

Further resaerch brings these conclusions:

CI&L 64C (2nd) 5194 10/47 E878

ATSF 32A (2nd) 8618 10/48? E1197

ATSF 48A 6631 10/52 E1222

Note serial 6631: This was ATSF 32A (1st). Damaged (by fire or explosion?) 1949, replaced by 32A (2nd) within three months OOS, then rebuilt as F7B, sold to ATSF in 1952. Boy, does that make it suspicious of being 1950C! Time frame right, model right (passenger F7).

LNII-262 has a note of NP 6550 being ex 1950C, but I suspect this is incorrect. Serial 15683 in sequence with adjacent NP F7's in order 3134.