OEM casting numbers are notoriously hard to make out, 3 or 6 can look like 8, 5 like 6, and vice versa, etc..
If you're positive of the crank casting numbers, then that's where I don't know- I do not show any Chevy cranks starting w/"8", although the number does somewhat resemble a generic-type GM part/casting number. The vast majority of Chevy crank c/n's are 7 digits long, and begin w/"3".
I'm not doubting what you thing you're seeing, AFA the stroke. But there are a couple things not adding up... I looked all the SBC 3.75" aftermarket cranks that Summit sells (Scat, Eagle, Lunati, Summit, Howards)- no matches there, either.
So, given that- plus the piston number showing up as a 350 cid pin height piston- leads me to believe that the crank is from another maker than the ones I checked on, a mistake was made measuring the stroke, or a slight chance that the rod journals are offset ground to give the stroke increase you measured.
Last edited by cobalt327; 08-23-2010 at 11:39 AM.