You made me look, MH ..... Why are there two wear patterns on the back of the #5 main cap in the 2nd pix in post #30? Aren't the flywheel bolts at the same radial distance around the crank axis? So is the edge of the flywheel's mounting recess contacting the back of the rear cap? If so, why?
I also just checked the rear surface of the #5 main cap on an early 360 and a'68 273 block, and neither has the inner step on the back of the cap behind the rear seal area, as seen in that same pix......???? It is almost like the rear flange of the crank has been shortened or the rear cap is not matched to the block.