1918 Hudson chassis

I have a 1918 Hudson chassis (M 43461) . It has the round tube (factory riveted ) between the frame rails, forward of the radiator shell. I purchased this chassis for the engine which I intended to put into one of our 1916 model 640G hudsons. Although the rear mounts, rear lashes to transmission etc. are the same, the super six engine turns out to be approximately 3 inches longer..,.the extra length because of the 4th main bearing first added to the 1916 super six when the hudson crank was fully counter weighted thereby increasing its weight by approximately 40 lbs.      Jim Ryan