When I commented on the good idea of standardized rolling stock, I didn't mind either
forcing companies to use standardized rolling stock forms so much as I figured the railroads would want to build up their own fleets of modern rolling stock with just enough standardization to allow them to be used with each other. Every railroad is going to have different fleets out of different needs, but what I meant there was that every railroad would have their own similar car designs and purposes.
On the ideas earlier - lots of E-units and F-units had steam generators removed for freight services later in their lives IOTL, particularly among lines that either had huge fleets of such engines (like the Pennsylvania, New York Central, Erie Lackawanna and Baltimore and Ohio) or power-short roads (Illinois Central and Rock Island). My idea there was centered on reducing the cost of maintaining hundreds of refrigeration unit generators by having power lines stretched though the trains to the locomotives, which I think has real merit as many reefers were used in block trains owing to the perishable nature of their cargo. Yes, it would require surgery on the engines themselves, but is the cost in maintaining one generator and wiring better than dozens of individual generators? The generators would have to be kept for when the cars aren't hooked to locomotives, but reducing maintenance cost certainly has a benefit.
The compressor-equipped caboose idea was largely based on the fact that having the compressors all at the front of the locomotives would reduce brake response, and having cabooses equipped with such air compressors would both provide an additional aspect of safety and improve the train's ability to apply and disengage its brakes. Unmanned mid-train helpers didn't really become common until the 1980s, and while manned helped units were common until the 1990s (I vividly remember serving on them as a BN brakeman in the 1990s), particularly in the Midwest the trains both got very long and very fast, and having additional braking abilities at the rear end I would say both has benefits from a safety aspect as well as an efficiency one.
Waterproof is correct about the extra maintenance costs involved in this, but I'd still seriously consider both of these.
Besides, the PRR could hypothetically buy the diesel replacements at a cheaper price if they come second-hand.
Maybe, but many diesels bought in the immediate post-war era ended up serving their owners into the 1970s, even the 1980s in many cases. (Some after rebuilds lasted a lot longer than that - the Santa Fe's CF7s were effectively F-unit guts with a road switcher body on it, and quite a few of them lived into the 21st Century on bigger railroads.) Second-hand units wouldn't be all that easy to find, unless the Pennsy is prepared to buy units that weren't so much loved by their owners (such as many Alco products and perhaps even oddballs like the Southern Pacific's diesel-hydraulics).
What might work here is to have the Pennsy utilize their Altoona Shops (and the N&W's Roanoke Shops too) as diesel-rebuilding centers as the steam era winds down. As you have the Pennsy ultimately electrifying most of its route miles, having them buy second-hand diesels and rebuilding them to their needs is probably considerably cheaper than buying new, particularly if you haven't got diesels for trade-in. (Bonus here: when the time comes for GE and EMD to build electrics for the newly-electrified lines, you can use the diesels as trade-ins.) This keeps the huge facilities at Altoona and Roanoke working and reduces the Pennsy's motive power cost. And as Waterproof and SsgtC commented, going with ultra-modern steam locomotives to lightweight trains is in fact fairly wise, as you can have diesels for heavier trains that the steam engines would have difficulty moving. With that in mind, you'd be better to keep the steam engines on Lines West, as they tend to be flatter and straighter than those east of Ohio.
