The problem is that
"The motor was rebuilt in 1995 by the previous owner, but I believe it to be...." When somebody does that, unless you have the parts in your hand, you really have no idea what he put in there. It could have been single springs, dual, triple, beehive, or coiled up paper clips for all we know.
But, presumably, the rocker shaft is now off, and rope, or something, is jammed in the cylinder through the spark plug hole so he can now easily, and safely, inspect the broken spring, and maybe post some pics. Blykins' eye might spot something funky on the picture that would tip him off as to why it fell apart. I would just take the spring off the other valve in that cylinder and measure it and I bet somebody on the FE forum will most likely just send him a matching spring. It wouldn't surprise me though if some nice sharp pics of the broken spring/retainer/rocker might not show something to the trained eyes we have around here. And, if it doesn't, well then, "it was just one of those things...."
