You might look up the Onken design, because it sounds like that's basically what you have. The vent area is roughly equal to the radiator surface area, in the form of a long thin vent. It looks to me like what you have is about 3.5ft3 and probably tuned for 35Hz to 40Hz. I think it will work very well.The JBL E140 is pretty bass shy though. I'd consider it a midbass driver. When used in a cabinet like this, it will give you EBS response, with the shelf being -5dB from about 200Hz down to 40Hz. This is definitely going to need corner placement. If a corner isn't possible, place against a wall and as close to corners as possible. If used on stage, it will be bass shy, best for guitar or vocals.
The cabinet sounds like it will actually turn out very nice. You can spend your time making them cool looking and they'll be very nice, I think. Brace 'em well. It will be a versatile cabinet for you that will also work well with other JBL 22xx series woofers, like the 2205, 2225 and 2226. These later woofers won't be EBS, and will give more of a Butterworth alignment. All-in-all, I think you'll have a nice cabinet that will sound good and look good too.