[SFfiredog]

Hello,
A C8 "service" block is a later replacement block. These blocks were never used in a production line car from the factory. They are also known as "juice" blocks because of the oiling provisions allowing the use of hydraulic cams. These later blocks did have the squared off cylinder liners (stronger) and usually had the external ribs on the sides of the block. I would definately check for core shift and sonic check the bores as these blocks tended to have more casting inaccuracies than the '66 and earlier blocks.
--Mike