Just measured my shock tonight (bought a B12 shock for the B6 and swapping the B6 shock into the B4 for trials).
This is what I came up with.
Width of upper bushing/eyelet is: ~29.75mm.
Width of inside of lower buckle/clevis/fork/u-ey.. whatever ya wanna call it: ~30.80mm
I measured the length of my shock from bolt center to bolt center at: ~306.2mm.
Both upper and lower bolts are 10mm diameter.
Hope that helps.
No idea on the spring rate? Sorry.
BTW.. the B6 shock measured right at 315mm center-center..