What were you running before? The 7psi difference could possibly be from the 40 weight oil

When I bought this thing it was a quart low, and I just added some 10W30, and then a bit later an oil change with the same stuff.

And I was surprised to learn that it had flat tappets this late in time. Amazing to me that there isn't a history, that I've heard of, of cam & lifter failures.

That is exactly what I posted....just in a different context.

I don't remember you mentioning this before! Yes it's probably both that did that.

Changing filter adapter seals won't increase your oil pressure. It may stop them from leaking, yes, but it won't change the pressure. It is most likely from your change to thicker oil.

Yep, exactly. I was comparing his use of 5w-40 to the "baseline" 10w-30 that the manual recommends. He was concerned about flow on startup in cold temps, and I remarked that 5w-40 oil would flow better when cold than the "baseline" 10w-30, and that I would be more concerned that the 5w-40 might be too thick at operating temps compared to the "baseline" 10w-30.

I think we're on the same page in terms of the oil technicalities, but perhaps my phrasing was confusing. Does it make sense now, or am I talking out my ***?

It was designed more or less during President Johnson's term, with parts dating back to Truman. (that should throw Salad off the timeline, lol)
Packard was doing roller tappet V8's in the '30's, but they were not common.
Very low spring pressures and a low-revving engine are easy on the cam, even with low zddp oils. I don't believe I've seen one wiped either, despite plenty of them getting el-cheapo quicky-lube oil changes.

Yeah, true about the old Packards. A friend is restoring a '38 Packard, a big long convertible 4-door, with a V-12 engine, and build like a truck ! It's the one with the chrome dome nuts holding the heads on. He said it had rollers, but in an unusual way. I didn't see it before he bolted the top cover back on.
And it runs really nice !

Maybe a Twin Six. Three rows of chrome nuts on each side? Beautiful motor.
It was an unusual design but smooth running. See x-ray cutaway:

Very interesting setup. I like the single cam driving the 90° bent rockers and GIANT valves.

I'm assuming that twin six here means two V6s bolted together?