I have had both. I like the Postwar motors a little better. As stated, cost of the Postwar ones is high. So I have a PW 400, 2559 and a PW celebration 2550.
The one thing I do on the modern and even some Postwar versions is to get the wheel bearings on the non-motor trucks to stay in place. In my mind the brass bearings should be press fit in the truck housing. Some are a slip fit so they may turn in the housing along with the axle. Also they move sideways along the axis of the axle changing the wheel clearance or centering a little. You may never have a problem running them, but if you do the fix could help.
I had one axle out of 24, that was so bad with the slop the bearing could just come out of the truck housing and drop the truck housing on the axle or jam the wheel. That is what triggered the "fixing" of these bearings for me.
What I do is to make sure the bearings are all the way in to the shoulder, so the wheels have the correct side play. If the bearing is loose in the truck, I add a very small amount of epoxy on the outer part of the bearing, inside part of the truck. To hold it to the truck truck housing. I use a tooth pick as an aplicator. A small bead for about 1/4" is all you need. Just enough to keep the bearing from sliding around. Don't get any on the axle! Make sure the bearings are held in place until the epoxy dries. Jamming a toothpick between one wheel and bearing usually works to hold both sides in.