Union Pacific "FEF-4" data?

In an article on Union Pacific 4-8-4 steam locomotives in "Classic Trains Special Edition #2 - 2004," W. Kratville reports that the Union Pacific went through two cycles of trying to define characteristics for a new class succeeding the FEF-3: once in 1942 and again in 1945.
First time around the boiler was to get a somewhat bigger firebox and combustion chamber. (Also a quadruple stack front end.)
Second version was to get a larger fireboc (apparently larger than on the 1942 version) with a "larger boiler" (larger how? diameter?). (Also poppet valves.)
The article doesn't, however, give numbers: hom much larger was the firebox to become, how long the combustion chamber, and if the final version was to have a significantly bigger boiler (Niagara-sized? ATSF 2900/N&W 600 sized?), what were its dimensions to be? (And who held down the chief civil engineer when the new axle loading was announced?)

If anyone has information on this, I'd love to hear it!

(Also posted to Union Pacific forum.)

I can't recall where I read it, but I was under the impression it was also considered to have a 3-axle trailing truck.

It might have been in conjunction with an article on the Allegheny I read somewhere... if I come across teh source, I'll be happy to give a reference.

jgallaway--
If you do find that, I'd be very interested! There was no hint of a three-axle trailing truck in the article I referred to, but-- given that U.P. seems to have had more stringent axle-loading requirements than some railroads (my wisecrack about holding down the civil engineer was based on an impression I have gotten over the years that U.P. tried to keep axle loading on its steam locomotives lower than that tolerated on a number of other railroads: the fact that an FEF-3 is smaller than, say, an ATSF 2900 is just one of many hints), this might have made sense.