Just saw this thread @laming I would try a ZW-L (ZW-Legacy) or K-Line "power chief" transformer. These put out a "chopped" waveform that looks like a shark's fin when viewed on an oscilloscope. The resulting inductive "kick" will coax a little more out of those old 3-pole motors. Brighter lights and better smoke too if that matters to you. The trade-off is more buzzing and more noise. The K-Line transformers start at less than 4 volts, but pretty much any postwar loco needs at least 5 volts to get moving so not a big deal.
Because the gears are back-drivable, two motors or two locos can actually "help" each other, giving a reasonable number of power pulses per inch. A dual-motored diesel, or even two single-motored diesels in a consist will give near-scale speeds, at least when pulling a load. My first MTH can-motored diesel (no speed control) was quickly relegated to the shelf because vintage Postwar power actually gave more realistic performance on our sharp curves.