Just a simple thing I wish manufacturers would do...

[Lastrites]

My Odin tunable gas block has such a line etched into it, you still have to mark the barrel for tdc. I get where your coming from but it's not to difficult to strike a pencil line on both the block and barrel, I usually pencil a line on both block and barrel in front of and behind the port for two reference points. Prior to that I remove the set screw underneath the gas port and install it upside down to measure the offset from the shoulder as well.