rear hub size
 

I want to install a S/A 2sp. hub on a frame that has chain stay spacing @ 112-114 mm. I can only find a S/A hub that is 116mm. Can the spacing of the seat stay be opened up to accommodate the added 2-4mm?

What kind of frame? Assuming it's an older steel frame it should be a piece of cake.

the frame is an old pre Raleigh Hercules frame. I presume 26". I tryin' to kinda fix it up to see what it will look like!

you may be able* to find some thinner [or thicker] nuts and alter the overlocknut width from the left end.

* I would be able to pursue that , I cannot project it for you.. ask at your friendly LBS..

The difference is well within the spring or flex range of your rear triangle. So if you don't mind spring the frame open a bit each time you install the wheel, you're good to go as is. OTOH, if springing the frame to mount a wheel bothers you, which it shouldn't) you can bend, (cold set for the verbally squeamish) the frame to permanently spread the rear triangle. This is a straightforward job, but some care need be used to ensure that you bend each side equally, preserving the bike's centerline.

My advice, is buy the hub or wheel and see how it goes, then spread the frame (cold set) if you find the springing bothersome.