I have the MTH CB&Q E6 ABA set from a few years back. I actually corresponded with the MTH designer & supplied him with photocopies of prototype material. I explained that although the Q never had E6s, they did try to order them during WWII but the War Production Board vetoed their order.
I suggested two paint schemes to MTH:
1. Decorate like an E5 with parallel stripes along the sides to simulate the fluted stainless steel sides of the E5 prototypes. The Q actually used a similar "shadow-line striping" on some smooth sided passenger cars and an E7 to simulate the look of an E5 on smooth-sided E units, but instead replaced the silver-painted steel side panels with smooth-sided stainless steel side panels on some E7s, E8s, and E9s. (MTH did not like this option because they said that narrow-parallel paint steps are hard to reproducibly manufacture.)
2. Decorate the E6 model with the prototypical CB&Q E7 paint scheme: silver paint, smooth sides, red single stripes just above the bottom of the carbody & below the cab windows & side vents, "BURLINGTON" on the sides in Zephyr Gothic Font, black "window" & "vent" striping on the nose, full color BR herald on the nose, and silver Blomberg trucks. Because this was a "fantasy" engine, I suggested that they number the units 9998A, 9998B, & 9998C because the Q only used numbers 9900-9997 on their prototype E unit Zephyr fleet. MTH used these suggestions on their model.
Hope I am wrong, but this is probably the closest that we will ever get to a 3-rail O-gauge CB&Q E5. It is an awesome model to my eyes.
CB&Q Bill