Factory spec for all Small Block blocks is 9.025".
Piston manufacturers use a deck figure of 9.000".
You might indeed encounter a block with a different deck. That's why you hear about fellows milling the deck of the block to achieve the proper piston to head dimension (squish). Aftermarket pistons are usually shorter from the crown to the centerline of the pin to accomodate this milling and allow for it. That's why you must be extremely vigilant in measuring everything before assembly.