There are no mentions of it in "New Products" or anywhere else in the magazine, only one ad.
I have no access to a scanner, so I cannot post the ad.
Here is the text:
NEW ARRIFLEX 35 MODEL II B
400 FT. COLOR MAGAZINE
(takes 480 ft. of black and white film) with collapsible take-up core, new take-up mechanism, new loop-protector for storing loaded magazine.
STRONGER HANDGRIP MOTOR
more power to drive the new, larger 400 ft. magazine.
MORE EFFICIENT ADJUSTABLE MATTE BOX
with geared filter stage.
FAMOUS RUGGED ARRI RELIABILITY
ARRI MIRROR REFLEX THROUGH-THE-LENS FOCUSING AND VIEWING SYSTEM
ROCK-STEADY FILM MOVEMENT
Okay, the next year the variable shutter IIB came out and was accompanied by press releases and more than one ad.
so judging by that, the new features listed here and the lack of any press releases it seems safe to assume that the differences between the 35IIA and the 35IIB are the new accessories, and maybe minor cosmetic changes not considered worth mentioning.
& it seems that the 35IIA can be upgraded to a 35IIB.