Roy
I think you have verified an issue here that I have been pondering............
I have run into fitment and tolerance issues on the Regulators before.
Hmmphh..........
To address your question, the hardness is not an issue but the nickle plating may be.
I would have someone "reverse" the plating off first. This might even fix your fitment issue as you said.
Then I would measure the depth of the bolt stop cuts to see whether that will cause an issue with having enough stop to work correctly.
I have put many Uberti cylinders in other clones and even in a few 2nd gen Colts. The Uberti cylinder is the largest diameter of the bunch!
Regards,
HH