It doesn't seem, from the picture, that you would have a gasket leak into the combustion chamber. But it may leak at that cooling port, to the outside of the engine. If it was mine, I would deck it. Also that way, you can check it for square, and be sure, both decks are the same. Also depends, what your intention is for engine. A lot of guys want to deck a 383 to get the compression up..There...you have my 2 cents...I would deck it.
Have shop check it to see how much it needs cut to clean up, might need a lite surface or could need a bunch, not saying a good gasket wouldn’t seal it but I’d hate to get it all together in the car and have it leak
All parts are machined with different tolerances. So every case is possibly different, I had a 440 block decked 10 thou and the intake needed milled to fit properly. But the heads were also shaved 5 thou so that played part too,
But depending on how much needs taken off it can also change pushrod length, also be sure to check p2v clearance since the piston will be closer to zero deck when milled.