I've studied "CE" block stampings for many years, and have accumulated a sizable library of "CE" stamp images from Camaros and Corvettes while doing so. My research indicates that a letter ("A", "B", etc.) following the year of manufacture digit indicates a second ("A") or third ("B") trip through the originally-assigned block of "CE" numbers, and Flint V-8 was also later assigned a supplementary block of numbers (90000-99999) in addition to their original block of "CE" numbers (20000-49999).
The "CE" replacements were furnished as both short blocks and as "fitted" blocks (block and fitted pistons, no crank or rods), but the vast majority were short blocks; it was rare to blow one up and not damage the crank and rods.
The "CE" block in my '69 Z/28 was dealer-installed in June, 1970 (using one of its original 186 cylinder heads and one new replacement 186 head with screw-in studs and guide plates), with all the original bolt-on parts (intake and exhaust manifolds, A.I.R, alternator, distributor, etc.). It's stamped "CE0A96509", in the supplementary block of Flint numbers.