If I remember right, that analysis of the Uberti '66 was done of a small piece cut from one of the side plates and not the frame.
Maybe the same alloy?, maybe not.
It would seem that a mfg'r would strive to keep things simple though and use one matrl..
The newer repro rifles built on the old link-pin actions as the Henry, 66 and 73 were and now mfg'd in more powerful calibers (pressure) but still on what appears to be a '[brass' frame,,,I still believe one of the more modern alloys available like a phosphor bronze is used.
There are many high strength bronze alloys available now.
With the lawyers peaking around every corner of the industry looking for a free ride, it wouldn't seem likely that a modern mfg'r would place a firearm on the market with a simple old school bronze or cartridge alloy brass frame and then chamber it for something producing pressures exceding what that metal can handle.
I checked a little further myself just because the subjsect is interesting. The amt of phosphorus in the Phosphor Bronze alloys (of which there are more than a few different ones) seems to be less than 1% of the mix. Usually around .5% or so.
It's certainly not a major component but it seems to make a big difference along with how the material is work hardened and heat treated afterwards.
Interesting stuff.