For those keeping track, due to a rookie mistake on my part as well as a nod to my priorities, there will be a woofer swap on my project.
Unfortunately trying to shoehorn the Extremis 6.8 and the UniQ driver on to the front baffle of Dayton's 0.5 cu ft cabinet isn't going to work out; I didn't take into account that with the grill, usable vertical space is limited to about 12". I could go with the 0.75 cu ft cabinet, but that's a less elegant solution being 3" taller and 1.5" wider, with a lot of wasted internal volume, and it'd still cost me a few bucks to implement.
So I made an executive decision
Instead of revolving the project around a 7 year old pair of woofers, I'm ponying up for a pair of Seas L16RN-SLs. They're built on a 5.5" woofer frame, but have sufficient Sd and Xmax to rival a 6.5" woofer. With the modeling I've done, the 0.5 cu ft cabinet should actually fit like a glove, with a -3dB point around 55Hz and 10dB down around 35Hz. With the amount of low end gain I get in room, I'm predicting that will work very well.