The 801 Series Three as I have mentioned many times before, was essentially an 801 Series Two with my crossover fixes factory installed, and some ferrofluid damping in the tweeter.
Yes the stock series Two did have a boomy bass (and worse) without the AVA fix.
I still have the fix plans available as a free .pdf file if you PM me your e-mail address.
Plasti-clay man, plasti-clay, read all about it in the 1982 back issue set of Audio Basics, available a .pdf download at our web site. Tweeter apart? Pop of the outer grill ring (carefully or it wil break -- with the tweeter removed from the midrange cabinet of course) and then it will split open.
Frank Van Alstine