I think you will find that all modern K frames from sometime not long after the model 19 was introduced, have the same sized yoke and frame
I have a 19-3 and a 10-7 in front of me right now and the top strap on the 19-3 is .647 wide and .208 thick , the 10-7 is .650 and .206 thick. 19- 3 at yoke pivot including frame is .707 and right at ejector rod .640 10-7 is 7.06 and right at ejector rod .647 The 19-3 frame is .820 at the barrel and the 10-7 is .817
I just drug out a M&P 38 from 1951
Top strap width is .651 (wider by about .004 to .001) and .202 thick (.004 thinner)
Yoke/frame at pivot .706 (same as above models +-.001)at the ejector rod .648 (+.001)
Frame at barrel is .812. So it is, .008 skinnier there than the 19-3. The only real change if you considered .008 to be that much
I believe most of the small .001-.003 type differences could well be from final finishing. I have replace a yoke and found the new yoke to be maybe .001-.002 proud. They did change the front profile over the years and the top of the frame at the barrel varies with barrel type.
Another thing to consider on a model 19 over a 10 is that the top strap has had more metal machined off for the sight tang and the sight body. No way the top strap and rear of a model 19 is stronger than a model 10. LOOK at them. Measure. I know just how much material because I have machined it off to mount adjustable sights numerous times.
I know the yoke tubes are the same as I have fit a 2 model 19-3 cylinder to 2 10-7s and one to a 10-2
But over all the difference in frame dimensions from a pre model K frame 38 special to a model 19-3 357 magnum don't amount to anything at all.
I do believe the heat treatment was improved in the 50s, but I can see absolutely no reason that would not have occurred across all frames. Time and cost of a improved treatment over a poorer one being totally insignificant. (I do heat treating and had a friend who ran an industrial heat treat shop) Plus, inventory and liability reasons. I have also used my hardness tester on a bunch of frames, both blue steel and stainless and there is almost no difference there. They are all relatively soft. In fact you need to measure in the A range not the C range. Too soft for C. Their hardness is about the same a mild steel, but hardness is only a small part of the story. With a gun tensile strength is the big factor.
In other words my belief it the difference between a 10-7 frame and a 19-3 both structurally and strength wise is 0 ,Zip, Nada and I have 3 model 10s I have shot repeatedly with model 13/19 cylinders and I plan to keep on shooting them too.
