* Main Caps are the same outer dimension...just a smaller "hole" for the Crank in the 400 Cap = Stronger with Detroit wonder iron.
* Cylinder wall thickness will usually sonic test pretty much the same from a B 400 to an RB 440....but the "unsupported" length of the wall is much shorter on the lowdeck 400 Blocks = Stronger
* It could also get into some prevention of #4 Main Cap walk ??...nobody wants to hear this, but we always found the stock 440 1053 Steel Cranks much easier on the mains, especially #4, because of their ability to " winde" and " un-winde" down their length as they spin....as opposed to todays 4340 " NON Twist" Cranks which tend to transfer and hammer the Block harder, and they were plenty strong enough for our 700hp stuff back in the day.
