[x33rs]

On a proper rebuild, if you're particular about the details, it's almost always necessary to deck a block if you want things square.

I haven't come across a virgin block yet that is square, some even twisted. Even a brand new GM crate engine I have here isn't square and it hasn't even been run yet. Sometimes I come across blocks that were decked and still not square. It's also beneficial to have the piston as close to zero deck as possible for better quench, although on Chevrolets when stamps become an issue I usually spend the money on custom pistons and move the pin height.

But I'm one that is very picky on my engine builds and always looking to make them better than factory, even on a stock build. I just finished a 455 for a customer that came from what was supposed to be a reputable shop. It was decked. Was found to still be uneven front to back, had to take another .007" off.

Just tossing out some reasons why people deck these old engine blocks. 40 years ago no one cared about the numbers. The saving grace on some of these where the damage is already done is that you might be lucky enough to have an untouched vin stamp by the oil filter.