Hi and thanks AltecBest (apologies for not recalling your name), and others who commented.
The port is the size shown in the original A8 blueprint from the mid-60's. Later designs showed two tubed ports (A8C), which used the 3156(?correct) 16-inch woofer.
I once asked this board would a bigger port be better for bass and the general opinion was no. Certainly with the current complement of drivers and x-over it has more bass than before, and smoother overall low-to-high response. The MC2100/C28 combo helps too.
It's nice having a few different cabs and drivers around to mix and match, giving quite pleasing results on occasion.
-Jon