Thanks for the thoughts guys, sometimes when you roll the dice you get 'snake eyes'. At least I'm still rolling, I've already buried way too many friends, relatives, acquaintances that didn't make it to retirement age, or if still alive, can't do much of anything physical anymore, in pain or not. Doesn't mean I'm not frustrated/mad/bitter about the circumstances that has put me in this position though!

True, toy slot cars are made of polystyrene plastic, but since the late '60s all the racing classes I've been involved in use clear Lexan bodies that you paint from the inside and it just dawned on me that's what the various sheet material I have is, just thicker, with the thickest being the milky colored one.

There's a number of [expo] calculators on the net, but I've lost the links.
Googling:

Exponential Horn Calculator

mh-audio.nl - Expo Horn

Single Driver Website

This one you can use on-line or DL and if they haven't dumbed it down/'streamlined' it/whatever, an excellent one:

Ishtek
Ishtek

GM