Ah I see said the blind man as he picked up his fiddle and saw.
Good project and great reasons for getting started. I wouldn't restrict yourself to the 2235 necessarily , however since you have a plan that involves a large format horn you should be able to use the horn down to 5-600 Hz , to my ear at least this gets you away from the issues at the top end of the 2235's range.
Anyway since Lee has come up with one for you I would snag that and post a WTB ad in the Marketplace section and see what comes up. There will be one out there for you , just be patient.
That'll get you started at least and by the time you get your boxes completed I'll wager you have another at hand. Job done.
BTW all this is a fairy tale and worthless without pics , thats the rules around here. Good luck. M
Incidentally you mention that you have CNC mills to hand. There is a healthy stream of small machining jobs popping up in these forums , you know flanges and so on for obsolete drivers etc etc. You could be the go to guy. You could machine your own mass rings in any case.
I'll bet there would be some take up for acrylic phase plugs for slot tweets. Lots of our boys would like the 077 look.