340 K Member ??

I worked in an assembly plant for 31 years and maybe 5 or 6 of those were in the chassis department, frame line to be exact. Im thinking that since this seems to have begun all at once (in 1970) that the vendor for the K-members made a change to the dimensions during a model change over and the assembly plant didnt make a change to their tooling/fixtures OR vice versa. The washer could have been put there for a quick fix as a spacer/shim to correct the tooling/fixtures at the other end (assembly line). Being as this seems to be 340 engines only it could be that there was a certain operation to be done to that paticular model. Fixtures would be to hold something in place while a part was welded on, a hole drilled, an A arm held in place, etc etc and or maybe the hole in the washer was used for a "locator". This is my utmost professional educated guess LOL TYVM.