As shown at the link in my earlier message:

The A preface means:
+.005 cylinder bore
-.010 main journal
-.010 rod journal

I doubt if the GMC Maintenance Manual shows that engine code information, but it might and it should have the needed specification information.

I'd buy a GMC Maintenance Manual to match my year engine.
http://www.classicpartsusa.com/product/SM47G_1951/1951_Truck_Parts_Literature
http://www.faxonautoliterature.com/...k-Repair-Shop-Manual-Reprint-P25248.aspx