The prototype ACL engine had some part changes as well as the addition of the Worthington feedwater heater (FWH) system (only added to some of the 75 engines of their original USRA order). The FWH piping on the left side is based on normal practice, as I haven't been able to find any photos of that side of a FWH equipped ACL Pacific. The only picture I have found is of the right side of #1519.
The United model is basically well constructed and detailed, aside from a few areas. After cleaning up solder joints, casting flash, and straightening parts on the PFM engine, I added the FWH system, replaced or added a lot of detail castings, piping, and other parts, improved the drive with NWSL ball and cup universals, and added my unique loco-to-tender hoses. The lead and tender truck tires, plus some valve gear parts were recently nickel plated. This and more changes and additions to the PFM base made a nice replica of these unusual ACL locomotives. I still may add a diode driven headllite bulb.
'Model Railroader Cyclopedia Vol. 1 - Steam Locomotives' (Kalmbach)
'Atlantic Coast Line Railroad' by R. E. Prince
Mainline Modeler - August 1987, p61 - 'USRA Light 4-6-2'
Trains - March 1991, p30 - 'Uncle Sam's locomotives'
'Standardized Locomotives for the US Railroad Administration' American Locomotive Co.
In progress shot of the ACL Pacific