A 1970 Chevelle with the L78 and the optional 4.10 gear would be coded CKK. The LS6 got a different posi unit, thus the different code of CRW.
I think you're right about the CKK 0627B rear being for either an early 70 Chevelle or possibly a late 69.
I could use a CRU coded rear for a 70 Chevelle.
That's a 3.31 Open rear that has the HD differential for an LS6.
If he doesn't have that, I'd settle
for a CRV coded 3.31 for the same car.
__________________
Rick
69 Chevelle SS396 Silver L78 M21 Post Sedan (Berger Chev.)
69 Chevelle SS396 Black L78 4-speed 4.10 Post Sedan
Don't text and drive.
Somebody's life may depend on it!