After reading the build sheet that I got with my 57 Bird years ago, stating 40 overbore and 20/30 under crank I was surprised to see the pistons (Conformatic?) stamped STD when the heads came off. I measured the bore and it is standard 3.80. Then I pulled the cap off a rod and the journal measures approx. 2.1750. The main caps and the rods show ECZ, the crank has the cutout with a 5/16 dot. The bearing inserts are normal without any wear. Always have had good oil pressure. Is the crank rod journal undersize from 2.1880 down to 2.1750 a problem? What bearing inserts were used to get this to work? I am using digital calipers to measure so can I be off by a lot?

57 Black Tbird 312/auto

Update: I went through measuring for the umpteenth time and took an average which puts it closer to 2.1780. Looks like it a 10 under rod journal. Haven't done the mains but pretty surprised by this given the spec sheet I have. Obviously, the engine I have is not the one listed on the build sheet. Don't have 2-3, only a 3-4 micrometer but I am getting stoked at what I have here.

57 Black Tbird 312/auto