Careful AB, his internals are date coded 1974, and use "pipe and plate" alnico motors. 9849-8B uses all ferrite motors, introduced prolly sometime in 1979-80.

AFAIK, the history goes something like this:

9849A originals used a foam edge woofer, sealed box, and 900hz XO.

Sometime not long after their introduction(very early 70's) came the 414 and ports. The move to a 1500hz XO may or may not have happened at the same time.

Sometime late '74 or early '75 the 9849-8A was born with the newly designed cast return pots on both HF and LF sections.

9849-8B arrived circa 1979-80, and with it's new ferrite motors offered a big step up in sensitivity and sizzle at the cost of some midrange smoothness and warmth.

This is my .02 based on the info i've been able to glean over the years combined with owning multiple 9849's, temper it accordingly.