So I tried these Stage 8 fasteners. I think they're great! I've driven a couple days with no header leaks or issues.

Now I can say there are no concerns about the strength of the nut thing. It's hard to see in the previous picture above, but the thing that acts as the nut is plenty thick - the threaded portion is probably the same thickness as a typical nut. No other nut or additional hardware should be used with it.

The length of the nut thing is just barely long enough to work properly at the large flange that's just in front of the cat. But they work!

It was probably faster for me to install these fasteners compared to regular nuts and bolts (or all-metal lock nuts) because I usually have to struggle with 2 wrenches or ratcheting wrenches in very hard-to-access areas with the headers. The Stage 8 fasteners only require one ratching wrench to tighten it.

I thought it was funny that the instructions from Stage 8 only mentioned their locking bolts. They didn't even acknowledge the nuts/bolts combo in this package.

If anyone else is reading this regarding TRD headers, it's fine to use the shorter 1" version of these. I had measured that I would need at least 1.25". But the way these Stage 8 nuts are, the threaded portion of the "nut" extends out a bit. It's possible to use less length on the bolt compared to regular nuts. The part of the nut happened to fit inside the hole in the flange, which also helped to keep it perpendicular to the bolt to start threading it. Then the bolt didn't need to be nearly as long, even with the thicker graphite gaskets.

I'm glad I cleaned out all of the old gasket material at any of the joints so the Remflex gaskets can do their thing.