What block size is in the 2002 Chevy silverado 1500hd 6.0L?

The 2002 Chevy Silverado 1500HD 6.0L uses a 5.3L engine block, not a 6.0L. There's no 6.0L in that year/model. The 6.0L engine was introduced later in the Silverado lineup.

Therefore, the question about block size is irrelevant to a 2002 Silverado 1500HD with a 6.0L engine because that combination didn't exist. If the truck actually has a 5.3L engine, the block size would be roughly the same as other GM 5.3L engines of that era, but precise dimensions would require looking up the engine specifications in a service manual.