What year did Mopar start stamping HP on blocks?

I think 67. MP was stamped before that. I not 100% positive on that date.

I have a 64 383 block stamped HP.

Yeah, that's why I'm asking, I have a 66 383 block with HP stamping along with a P that I suspect means premium fuel.

My 1965 Sport Fury 426 was stamped HP but in a much larger font than later years. THIS IS NOT MY CAR, but it is very close to what I had.

I have a '64 413 HP block as well.

The P did mean premium fuel.

I think at one point chrysler had 2 4bbl 383's a 290 or 300HP and what I'm googling was a 325 HP ... in 68 and 69 the 2 383 4bbls were 330 and 335 ... they only put HP on the higher HP engine . I had a 68 Sport Satellite 'vert that was a 330HP 4 bbl car , original numbers engine , no HP on the pad , but it did have the P for premium fuel as it had the same compression ratio as the 335HP road runner engine.

i believe some of the 413 blocks from 62 were stamped

there was a 1962 model year 383 stamped HP on facebook the other day ..... consensus was: it was from a dual quad 343hp engine

All the 1963 Dodge and Plymouth productions cars that came with the 426 C.I. motors were all Max Wedges, either 415 HP or 425 HP. All the 426 race blocks I've seen, both 1963 and 1964, had a lot larger numbers stamp on them as already said
1964 was the first year of those weak ass 426 street wedges

My 63 engine had 426 TMPHC iirr but really there’s no difference in any block from HC to non HC, just what’s put inside

Many shops and dealers sadly have the correct stamps and stamp "HP' on RBs Bs even small blocks lol

T stood for 1963
MP was maximum performance (max wedge I believe)
HC was the high compression version, 13.5 vs 11.5 I believe

At least that is what I recall from playing around with them back in the 80's.

You are correct about the actual block differences though, none.

Thanks, you nailed it. Wish I had it back, sold the whole car in 78 for $2800 lol