From your description, it sounds like one of the cabs is a 200S (horizontal port between the drivers, rear loaded drivers with a removable back) and the other is a 215S (vertical ports on the right side, front loaded with a removable grill). IMO either one is fine; I have both and don't really prefer one over the other tonally. I get more use from my 215S cab because it front loads just about any 15" driver, while the rear mounted 200S will only take small diameter magnet, shallow framed drivers (such as the AlNiCo JBL's) because of the port ducting. I doubt that an E140 will fit in a 200S cab but I've never actually tried.
The D & K series are very similar, in fact the frames and motors are identical except for the gray vs black crinkle paint and badging. The E series is a ceramic magnet, however the cones, while different in composition, suspension, VC, etc. are interchangeable between all of the drivers you mentioned. I personally like the way AlNiCo JBL's sound with tube amps. The D series sound great but won't take a bunch of power, my favorite is the K140 for my Sunn cabs.
There have been numerous posts about the various JBL drivers in this forum over the years, try a search and you'll get all kinds of good JBL info.
Also, I would be interested in the side ported cab if you decide to pass on it...
