Neither the 300 or 380 hp crate motors used the R/T head according to your information. Only the 402 crate motor used it and no one was talking about that engine.

Neither the 300 or 380 hp crate motors used the R/T head according to your information.

No, one version came with the upgraded R/T heads till they ran out.

Worked there almost 9 years, still remember a few things.

Springs, locks and retainers were changed on the .501/.513 cam variants per BOM.
You absolutely do not want to run that kind of a cam with the wimpy stock valve springs.

At the start, The entire engine (not just the block) began as production pulled just for us,
The parts added/painted Orange at Cummins recon. These were generally good values but were not
At all “race engines”. Race engine builders would sometimes tear them down and complain the clearances were
the same as a 1999 truck engine. Go figure...that’s what they started out as.

When production stopped, we then ate up OE service long block stock. Slight cost increase.

When that was gone, we ate up OE service short block stock and added OE service heads.
It cost more, the price went up.

Then we ran out of OE heads and tooled up the magnum r/t iron heads.
They flowed better than stock. With the r/t head swap, The 380hp variant pulled easy low 400s in testing and was
Re-rated to 390hp. The magnum r/t heads were not without issues, most problems were
Due to the type of tooling used to make them. I Could go on for a long time on the topic but it was
Somewhat Hobbled from the get go with the wrong type of tooling. Still, they had impressive potential
“For what they were” as articles and testing by Dulcich back then proved.

The price went up on crate engines again due to the heads’ expense.

The aftermarket noticed there were no OE heads to be had, and EQ tooled up.

Then we ran out of short blocks. The solution came from reman.
Reman drove the price up a whole lot. The price was high, and some were understandably
Disappointed they were getting a bored out rebuild instead of brand new.
The reman versions had a slightly higher perceived quality piston,
A hypereutectic, but most all other specs were the same.

Then reman kept saying they weren’t satisfied with
Core quality, and that 1 block in 20 was good enough for performance crate engine
Use. Personally I didn’t buy it. But Whether true or made up, they wanted out.

The last nail in the coffin was a super expensive deal, based on a brand new MP aftermarket race block version built
By a pro race engine builder. These were very nice pieces but the high price tag was a deal killer for most folks.
I always assumed more of these were given to show car builders for advertising than were sold.

Around this time a blowhard magazine writer who will go unnamed basically said Magnum R/T heads were overpriced garbage and EQ heads rule so RT heads were killed off, replaced by repackaged EQ heads. I heard about this and promptly collected
A few RT heads for later, just in case.

Now, EQ has also got rid of the product but some surfing shows a made in China casting that looks
Suspiciously close to the EQ, and of course the price is next to nothing.

The 4” stroke iron head version was probably my favorite, as the output made a lot
Of folks happy.

Looking back: some catalogued products you’d think were widely used were not popular AT ALL....
Other items that seem like almost stock replacement (iron heads) were actually pretty darn killer/sleeper products.

Yeah, that's a mighty high failure rate!!