I love all the old bulletins and stuff, they are fun, but might be best taken with a grain of salt.
They are Marketing documents at the core.
They want you to feel like a technical person when you're reading them, but won't provide any specific technical information.

Try flat lifters today and let me know how that works out....it won't be long, and they will be concave lifters.

This is the same group that sold the 1968 383 high performance by telling us it had "440 heads", as if
that was something novel and amazing. Meanwhile the 2 barrel engine had the same heads....

This is the same group that (later) gave us the heavier "6 pack rods" as a durability upgrade instead of addressing
the problem at the source (the boat anchor heavy pistons).

This is the same group that could have very easily crossbolted every Wedge block after the durability upgrade to the Hemi was
brought into production, but decided it would be better to save 75 cents.

Be careful you don't accept half truths out of love for the brand.

Notice they're saying it's a flat faced lifter but no specification is given.

Notice they're saying the cam lobes have less taper but no specification is given.

No specs=Marketing trash

How much was standard? Not saying.
How much was it reduced? Not saying.
Under what conditions is durability improved? Not saying.

Meh.

Very possible to sell standard lifter having a crown of .0015, and a "flat faced" lifter having a crown of, say .0011 that you purchased from another supplier,
create two different part numbers, and increase durability under one subset of conditions while potentially reducing it under others.
Marketing isn't going to allow you to mention the potential reduced durability at low speeds or wherever the compromise happens to be.
(There is always a compromise....with everything)

If the flat lifter and reduced taper design were so vastly superior under all conditions, why weren't they included in
every 440 HP after the dawn of the 6 pack? Surely it would have reduced warranty claims, but it didn't happen.
Why didn't the 426 HEMI....the ultimate, most expensive engine they had,
also have low taper cam and flat lifters? Why didn't the 383? Because: Marketing Trash.

It's probably more likely the 3 bolt cams were ground by another supplier who gave Chrysler a different taper spec by default,
it passed testing and "there you go: It is now a SPECIAL CAMSHAFT".
I've held the old prints for alot of these kind of parts in my hand, most of them say nothing and leave much to
supplier interpretation.