"Crossover Design for New Project"

[GM]

I had been looking at how to get the same bass reinforcement as AB is trying to do, possibly using a different Altec woofer, ala 421 or similar.

If you mean mid-bass only, then OK, but even in typical HE HIFI/HT apps, MI drivers should be avoided like the plague for bass since they audibly distort due to no real linear excursion to speak of.

GM