Rebuilding my forks

Anybody know how long the springs where when they were new, on a 1980 KZ1000 B4? My Cymers said they should measure at least 20.1 inches. They measure 20.5". I bought some used forks from a '78 because my original fork tubes have some rust pitting, and the springs from them measure 20.6", so I'll obviously use the longer ones.
I'm just curious as to how long these springs were when brand new, and whether I'd gain anything by adding a spacer as I've read about on other threads.
And the manual calls out to use 15w fork oil, so I'm also wondering if switching to 20w would improve anything.
Of course those emulators and Progressive springs sound enticing, but that stuff just isn't in the budget right now.

What problem are you trying to solve, is the front end too soft? I use 15W BelRay fork oil in my KZ650 and it works well for me even when riding 2-up. 20W may prove to be too stiff. If you find it is too stiff, you can mix 15W and 20W BelRay fork oil to fine tune the viscosity to suit your specific needs. Ed

Not really trying to solve a problem per say, other than the bike was diving down pretty deep when I hit the brake. Forks were pretty squishy. My biggest problem was my neck bearings, but I just put new tapered bearings in, and figured while I had it apart, I'd rebuild my forkas as well.
Just looking for some input from somebody that has switched from 15w to 20w and what they experienced.