Factory overbore

I'm not sure about the Letters,, but it was not uncommon to find brgs, lifters, and I believe pistons 1 and 2 thou over/under..

IIRC ma mopar had a shortage of cranks, and had to use some undersize.

As I remember those motors had a "maltese cross" stamped on them..

That was sooo long ago..

I believe you may still be able to get those 1 and 2 under brgs..

hope it helps