s4s4u Not arguing your point on this,,, and maybe you were lucky and just maybe you do not care or did not care about the barrel cylinder gap. Did both cylinders give the same measurement? Another thing is the timing,,,, even though Ruger made both cylinders and even if both drop in,, the timing can be off.
The boss being the same length or longer, doesn't mean that when fitted to the frame that it will have the same cylinder barrel gap. Some people this doesn't bother. But to some like myself I want the same barrel and cylinder gap and I want both cylinders to be timed correct.
In theory this sounds good and seems like it should work. I am referring to the stoning off the boss to correct dimensions. It does not mean that it will shoot straight or as well as the other cylinder. I am leaving out the variables such as dimensions, bullet sizing etc. And more importantly Wear!!!
If the OP has a convertible then it is much easier in this case for him to fit a frame.
It maybe possible with the new trigger and hammer that some timing may need to be addressed. Hopefully this will not be a problem. I have done this before and did not have problems. As a matter of fact my 44 mag Bisley with the 4 5/8 barrel started life as a plow handled grip frame. Ruger did not make these and I wanted one, so the work began.