Hi John,
I'm sending "B" the longest fluted .41 cylinder I have, and I think, with shims you'll be fine. I've used them and they worked well for me. Again, your measurement is the longest .41 NMBH I have seen, so just be sure to check the cylinder gap on all chambers/charge holes once the cylinder is in place to see how closely they match each other. That will tell you everything is square. A "range rod" is very helpful with a new cylinder also. That will verify alignment between the chambers and forcing cone. If any are out, it'll spit lead to one side, but can be easily fixed. If I can help in any way, just let me know.
Thanks,
jebstuart
PS, you may already know this, but use the "range rod" as follows:
Perfectly brush and swab clean the barrel and cylinder - the .41 rod is a tight fit.
If the rod drops through the barrel & all cylinders to the firing pin, no work is needed.
If the rod is stopped by any cylinder chamber but will drop through the cylinder to the firing pin when the cylinder is rocked back and forth by hand, no work is needed.
If the rod is stopped by the rocking cylinder and will not drop when lightly pushed, the cylinder is being stopped short or locked in overtravel by the cylinder bolt.
In this case; the easiest way to remedy the condition is lightly shave the cylinder bolt on the appropriate side 1/1000" at a time with a flat stone or fine file, reinstall and retry. A very little goes a very long way.
Looking from the back of the revolver, if stopping short of alignment, shave the right side of the bolt. If overtravel, the left side. It helps to mark a line indicating the exposed portion of the bolt, on the appropriate side (that needs a shave), that protrudes through the frame before removal. I use a razor point sharpie.
The tricky bit is to create just enough play in the cylinder to allow the rod to drop through the cylinder when rocked by hand. It will then self align when a bullet leaves the cylinder and touches the forcing cone. It relieves stress on the revolver and stops lead spitting.
That was a lot of jabber, but I hope it's helpful,
Jeb