So here's the pal nuts side-by side:
The original is on the left, replacement on the right. Although the photo does not convey adequately, it's a bit of an optical illusion in real life...the silver pal nut looks smaller and thinner than the original. In reality, it's only .5mm shorter, and the thickness of the material is similar. The interior diameter of the thread hole is also the same.
I guess the problem with getting it to thread properly lies in the different shape of the thread tabs. I was finally able to use a 10mm bolt with a tapered end to start the new pal nuts and shape the thread tabs.
The next issue was the torque involved. The engine overhaul manual says 8.1-9.6 foot pounds. I realize that small amount of torque is supposed to set the spring tension of those thread tabs, but the pal nuts seem to start deforming at that value. In addition, as I was torquing up one of the originals, it broke some tabs before I approached the prescribed torque range (are they one-time use items?)
...and yes, I've verified it's ft/lbs, and not in/lbs. I'm considering using an actual nut, rather than the pal nuts...there's plenty of thread on the studs for that.