This looks like our 15-180 Pivot Shoe. This shoe uses Series 190 Coil Balances. Can you clarify: does a single window sash weigh 42.2 pounds? If so, you'd need to use three coil balances on each side of the sash: (2) of our S190-840 8 pound springs, and (1) of the S190-540 5 pound springs. This would equal 21 pounds of support on each side of the window sash, for a total of 42 pounds overall--being within one pound of the exact sash weight should work just fine. Just be sure that's the exact sash weight before proceeding. Let me know if you have further questions.
I'm afraid this balance system can only use two springs per side, Mike. It's simply not designed to use two springs. That's one of the problems with putting in heavier glass on old windows; you might mess up how the balances are designed to work and paint yourself into a corner. The only way you can work around that is to just not put in glass that's heavier than what your balances can support. You really do have to work around them.
The setup I suggested before remains my best suggestion for a 42 pound sash. That works with two springs per side, but like I said you can't add any more than that. Two per side is the most you can do.
I've assembled a list for you on this page that contains all the items you show in your photos.
