Thanks for the tip, VOTT. Great to be here!

Mine are 8 Ohms. At least that's what they say on the backs.

I'm planning on swapping out just the caps first and doing a good cleaning on the pots. While I'm waiting for my new caps I might try your suggestion and start playing with the ports. I have a powered 12" sub-woofer with an active XO that I can set to pick up 40-50Hz and down, so getting the 416s down that low is not mission critical. I tend to enjoy the rumble of 25Hz more than the sparkle of 18K. And neither of them are as important as what these 811b horns are doing to vocals and acoustic brass and woodwinds. I'm tickled.

Like I mentioned in my OP, I built a set of speakers utilizing full-range drivers with a bass reflex cab and found not only the port diameter made a big difference, but the length of the port as well. Tough to add more after you've cut it off though! I installed Parts Express L-pads on them to level the highs down about -2-3dB so I'm familiar with them. They look like they'll fit nicely. Did you use the 3/8" long shaft, or the 1". I'm probably OK with the 50W version since I'm only pumping a whopping 3W/ch into them at the moment. It's a glorious triode 3W though!

Here are pics of my first speaker attempt and the L-pads on the inside:

8081002207_72373bd124_b.jpg8037582100_a841cb1ea8_b.jpg

When I get around to really overhauling, they'll make a nice back up set while the Heathkits are in the "shop".

FWIW, the full-range speakers, with a bit of HF attenuation, have an almost dead flat frequency plot from like 80-20K. And they sound pretty nice for what they are, but they do not have nearly the presence of these Heathkits, which I'm willing to bet have a far less sexy response curve. My point is I really don't care much for the numbers; I care about what I hear.