BFS works if you take your time with it and you have wheels that are designed for traction tires. It's far from perfect, but it makes the difference between a shelf queen and a runner when tires aren't available.
As for your prewar loco, a 3-car consist is just about all it was designed to pull. Back in the prewar days, most sets were only 3 or 4 cars, no doubt to stay at a price point, so that's what they will pull. Short of removing 2 of the drivers and finding a machinist who could put a groove in them, I don't know what to suggest. It might be worth asking Henning's Trains about it.
