Engine casting and stamp marks: what do they mean

[1973PettyBlueRR]

Am I have been looking but havnt found much information on casting and stamping marks. I believe I have a 383 but am trying to see what else I can find about it. I know if you look by the distributor and see a H stand it mean you have an HP motor. I believe I have a P. Anyone know what this means or what other letter or numbers mean? Thanks

 

[Pops1967GTX]

http://www.moparengineswest.com/Stampings.htm

P is Premium Fuel

Or you sure it’s an I ... might be an L for low compression...