You mean like this one?
Thunderer-Mason ConversionsBoth of these Thunderer grip frames came from guns, not just new parts from a bin. I think that is why they are a perfect fit to the '51 conversion frames. I have noticed that some new backstraps have been proud of the gun frame when bolted on and would require filing/sanding down to fit, which would then require re-bluing. That may not always be the case, but it certainly might. If you change a Model P to a Thunderer, you can keep the original triggerguard and just buy the Thunderer backstrap, but the brass Navy triggerguard will not work, so you will need both a triggerguard and backstrap. Now, on to the grips. The pearlite grip came with the gripframe, so it was already perfectly fitted. The wood grip had been mounted to a gun, but not this particular grip frame. I had the luxury of picking between several grips to see which one fit the gripframe best, and it is okay. It fits well to the backstrap and so-so to the frontstrap. I was considering sanding the grip to get a perfect fit, which would go through the finish and require refinishing. That's okay, I like an oil finish anyway. But I actually don't have these grips on the guns any more. They have been sporting the original Navy gripframes with Tru-Ivory grips. But I do really like the guns with the Thunderer grips, so I might put them back on now and then.
By the way, I tried putting the Navy gripframe on my Thunderer which gave up its pearlite grips to the conversion, but stopped when the triggerguard would not fit. The trigger did not fit through the slot in the triggerguard. The slot would have needed opening up towards the rear, and I didn't want to mess with it since it was going back to the conversion at some point.