Have fun with it! It is a hobby! Wont hurt but can be undone. If you are doing a rear port, I would suggest cutting a new back panel. Couldn't be easier and is quickly returned to stock. A port with the speaker positioned in the room correctly, may get you more bass. I doubt lower bass, just a couple spl from the woofer. Some feel the squawker is too bright, this may balance it out for you. Enjoy. 

Thoughts appreciated. Got some things on the way already so we'll see how it all goes. 

How does the depth of the La Scala AL6 horn compare to the Cornwall horn, especially considering time alignment? The AL6 horn, paired with an 18" woofer and passive radiator, can lower the crossover point and optimize the woofer for deeper bass.   For example, comparing an AE TD15H to a TD18H+ shows about a 5 dB increase in sensitivity. Although Klipsch would use its own woofer, this illustrates the potential gain in efficiency—great for low-wattage SET amplifiers, including those using 2A3 tubes.

Titebond III doesn't fully cure to the extent that type 1 or type II adhesives do. It remains somewhat pliable and prone to movement, comparatively. It may or may not be a problem IRL, but I've always avoided it unless I had a specific application that called for it. I've also found that it gums up sanding sheets more than types I or II. 

@gigantic, why not Titebond III? I've found that III gives a slightly longer working time to get everything aligned and clamped.

You could also put them face to face, reverse one channels speaker leads so the are out of phase... send lf freq.

I hook mine up before installing in the cabinet and run a low-frequency test tone at 10v overnight. Outside the cabinet, they're pretty quiet.

Well then, since you have wall terminals, I would use the multimeter to see if the wiring between the input and output wall terminals is shorted. Perhaps it's something shorted at the wall plate, and nothing to do with the speaker.

I'm a master carpenter and former cabinetmaker. I use Titebond 1 (red cap)  or II, (blue cap) but not Titebond III and never polyurethane or epoxy.  

Will be back later, so will have to test later today. Have to figure out where the kids went with my multimeter to test the other speaker, because I forgot to bring another one with me to verify against. Honestly, I 100% expected to test virtually no resistance because I was 100% sure it had shorted.   The receiver stayed in protection mode the first time I tried restarting it, before I touched anything. After I disconnected the speaker from the wall terminals, it worked fine. I would expect if it had been any issue with the receiver, or had caused damage to the receiver at all, that it likely still would have been acting up even without that speaker hooked up.   Hopefully, the issue will have been something pressing up against the connections, and the receiver caught it quick enough to protect everything. Not holding my breath though. Fully expecting to be down a pair of speakers for awhile.   I will update when I get a chance to test.