It may take some work. I assume the second model is a caliber .455. The barrel cylinder gap may or may not be ok. If it is too tight the front of the cylinder will have to be trimmed to open it up. Also the cylinder when the cylinder is opened will have excess fore and aft movement because...
Pre-war N-frame hammers and transition hammers (1946-1949) fit. I would try soaking it and scrubbing the single action notch in the hammer really well with a toothbrush. Problem may be with the trigger also.
It's fairly simple. It's virtually the same cylinder, except for a slight lengthening at the rear to accommodate the recessed case head, as the .38-44 cylinder for the Heavy Duty and Outdoorsman and the .44 Special cylinder used in the Second and Third model. The .357 was under development in...
For the cylinder stop spring itself, I have used part number 17185 the extra power stop spring. It's about half way down the page. I have not had a problem with the fit in any of my four or five screw revolvers.
https://www.gunsprings.com/SMITH+&+WESSON/K,+L,+&+N+FRAME/cID3/mID58/dID264#448
"I have run across 4 revolvers in 50 years that had the frame threaded at a slight angle, which in turn, makes the barrel at a slight angle to the frame. These guns cannot be sighted in. That may be something to check on this one, as it was so far off. You can put a straight edge along the sides...
Also, please note all the 8 shot N-frames have the frame mounted firing pin. It is very easy to move that hole. There are no alignment issues because the flat faced hammer hits the firing pin that has the correct location.
There were also the six shot .41 Specials on the L-frames done for John Taffin and others about 20 years ago. Those and the 646 makes one believe a six shot 10mm would be viable.