Rod,
If you want a loco to truly match the SRR "Crescent" locos, you'll have to go brass, or an older AHM/Rivarossi heavy pacific. The IHC version, IIRC, is actually a USRA light pacific, a locomotive the SRR never had.
The Ps-4's used to pull the premier passenger trains on the SRR (and it's subsidiaries), were all USRA heavy pacific clones. AHM did import a model known as the 1401, the prototype sits in the Smithsonian, but this model isn't quite 100%, as well as being very rare. The trailing truck needs to be changed to a USRA type, and some minor changes made to the tender. The regular USRA version that was imported by AHM would also make a reasonable model, provided you wanted to do all the detailing that would necessitate. Probably the cost of the details would push the price above a correct brass one.
With prices of older PFM Ps-4's being between $200-$300, and the newer versions for higher, starting with an older brass one would be more feasible. The only changes needed to it would be installation of a new can motor, possibly a gearbox change, and some detail upgrades. There generally seems to be one or two for sale on E-bay all the time, and it seems that used brass dealers generally have several for sale as well.
As to the prototype, there were actually 2 "types" of Ps-4's out there. One was a straight USRA heavy pacific clone, had a smaller 4 axle tender, and a Worthington 3-B feedwater heater. These weren't as well known as the later Ps-4's, which were the same USRA clones but had the Elesco feedwater heater, and a 6-axle larger tender, and the detail is excellent, with the only changes possibly in the headlight, depending on which year the model was imported. Precision Scale Company imported both versions of the Ps-4's, but they aren't as "cheap" as the ones from PFM. (Anywhere from 1.5 to 3 times the price of the PFM version). I have 2 of the PFM versions, and I think that although the detail is slightly better on the PSC versions, the PFM appears to be more ruggedly built. It was designed to run!