What are these marking?

Demonic said
I know what the markings are. Those are the engine bore specs carried out to the fifth decimal place. They are only published in the FSM for the 426 Hemi. Example- 69 FSM, page 9-98 Cylinder Bore (standard) "A" Size 4.24975" "B" Size 4.25025, etc. There must have been more information at the engine plants for all the engines.

I found the same thing when I re-ringed my 383. A testament to Chryslers engineering and machinist history. They must have had a piston-sorting system that was very precise. They measured the bores out to four or five decimal places, and the pistons as well. A slightly larger piston was matched to a slightly larger bore. We're talking about a range of .002. the 426 Hemi section lists 5 sizes, "A" through "E".

When I worked at Trenton Engine (Chrysler engine plant in Michigan) I had to run the boring line, the rod line and the crank line. I had to do that for every block and crank I ran off the line. (I was on the RB line for a year, hemis were a line you couldn't get on unless you had 20 years seniority , I had 2) I watched (in awe)women on the piston line ring pistons(4 to their 2) faster than the guys could slam them into the bores of the blocks and they were shooting 2 at a time into the block. thankfully I got moved to another plant and off the "grunt" production line. Glass is much lighter than /6 crankshafts