I have a '79 Hunter 30. The four forward most ports are 5x12, the two in the forward part of the cabin are 7x15 and the two aftmost cabin portlights are 8x18 manufactured by Gray. I just replaced all of them and ordered them through this site. They are exact replacements and fit the existing cutouts perfectly.
I am not familiar with the '76 model but I think there was a recent discussion about the differences in the portlights in the 70s.
The prior thread is titled: 1983 H30 9 Port Light Sizes
There is a discussion about the different size ports in different year boats.
