Here is what I have in 1 of my reference books.
Other letters and symbols may aooear on these pads. If not, it means the block has standard cylinder bore and bearings. On big blocks and Hemis a maltese cross will indicate 0.010in undersized main bearings. Any #s following the cross indicate specific bearings that are undersized; all others are standard sized. The letter X after the cross means that all of the mains are undersized 0.010 in. If the letter R appears it stands for rods and the same will apply as with the mains. The letter B means both Rods and mains are undersized.
The letter A on the pad indicates an overbore of 0.020in. Otherwise it is standard.
A diamond symbol on pad indicates that all tappets are o.s. by 0.008in.
Hopefully this is acurate info the book actually bounces between 0.001 and 0.010 without ryme or reason so...