I've ported several of the 983 heads and have gotten similar results. You need to open the intake ports same size as the counterbore for the alignment rings. You will also likely break thru into the head bolt holes adjacent to the ports.
As for advancing the cam lobes seperately, that was done for an entirely different purpose, and only needed if using real high lift roller cams on the later 250 and 292 style engines. You would never need to do this with the GMC or Stovebolt engines.
