Greg, could you give us the dimensions of your cab?
I'm looking at building a similar full range with crossover using a JBL 15" and a JBL 10". I will probably use a circular port rather than a vent as it's a little simpler.
Also, what silver grill cloth did you use? did you manage to find something close to Sunn spec?
When viewed as in the pics I posted above, the width is the same as a 200S head, the height is the same as the width of a 2000S head, and the depth is the same as a 2000S cabinet. This allows the cabinet to work with a 200S head when upright or work with a 2000S head when flipped on its side. So it is 24" wide when upright, 30" tall, and 15" deep. The port is half as tall as a 200S or 2000S cabinet, and it is the full width of the cabinet just like the Sunn cabinets. The back of the cabinet is angled on the bottom like an Ampeg SVT cabinet and the port just follows that around into the center area of the cabinet. The back of the speaker is baffled just like a Sunn 200S or 2000S cabinet. The port isn't that hard to do but a round one would be easier. Just be sure to size the port so it is the correct size to get the frequency response you want.
I added those small 6 inch speakers with a crossover network that Conrad made for me, but it is a bit harsh with those, likely due to the speaker choice. I may try some other speakers one day, but for now I use it with those disconnected and just the 15" JBL E140 speaker. Those speakers are heavy but they sound good. You could likely get a nice sound with some of the Eminence offerings too, or buy a used JBL like I did.
The silver grille cloth on the cabinet now is just the Fender stuff. It looks way better than the oxblood did, though it doesn't look as nice as the old style grille cloth that is on my Sunn 2000S cabinet. Unfortunately that stuff is not available anywhere anymore.