What does the "R" stand for?

[RonLiv]

On a another page a guy posted the stampings on his engine and thought they were unusual and wanted to know what the "6 23" meant . I got sucked in and told him that's a date stamp and I thought the stampings looked normal to me, very similar to how my engine is stamped. I did comment that I could not see the right hand corner due to the photograph cuts it off where I have an "HP" stamp. But in the left hand lower corner he has an "R" stamping. Since the only research I've done is on my specific engine I am not familiar with this code. I don't have this "R" stamping on my engine. Another guy said that means "regular" and that this is a non-HP 383. Made sense to me "R" - "Regular", what do I know, obviously not much. Another guy chimes in and says "That's not what the "R" stands for." But he fails to tell us (me) what it does stand for.

What does this "R" stand for?

 

[droptop]

Regular grade fuel. Most likely a 2 barrel engine.

 

[RonLiv]

Another guy posted this, so yup Droptop, the R is for Regular! Thanks!