You may have Isomat NG37 as shown on the Rig Rite web site. Rig Rite is very helpful because it lists several mast manufacturers and references the boats where the masts were provided. You just have to do a little hunt and peck. Newport sailboats go by their manufacturer name "Capital". Sailboatdata is also helpful so that you can find PEIJ dimensions, but they don't tell you the mast manufacturer or if the boat is deck-stepped or keel-stepped, so there is no way of knowing exactly how long the actual mast section needs to be.
http://www.rigrite.com/Spars/Isomat_Spars/Isomat_Masts/NG37_mast.html
The way I see it, the mast manufacturers must have standardized lengths made up by a company that extrudes the aluminum in the desired section dimensions. The mast manufacturer must then customize the lengths to fit the orders from boat manufacturers. I'm sure that's the simplified version. The same cross section seems to be used in Newport 27, 28 & 30 but I'm guessing the lengths are different depending on the model.
BTW, I love the Newport 30. I was first introduced to "large-boat" sailing on my aunt & uncle's Newport 30 in Chicago in the late 60's. I thought the boat was about the coolest thing I'd ever been on in those days and it was the biggest treat every time they took me sailing.