Curiouser and curiouser...
I thought the Vishay BLH site said they were located in Canton, and the address Ihad for BLH Electronics (and then Thermo BLH) was 75 Shawmut Rd. in Canton. South of Boston, not northeast like Cambridge (or Waltham, which is virtually next door to Cambridge)
Meanwhile, I thought the facility in question was a different one, at 42 4th Avenue in Waltham. (I actually have GPS coordinates for the site: 42.393436 N by 71.260267 W). This was built in 1957, and was in active use as late as 1985.
Unfortunately, it appears that this facility was demolished in August 1989, and a hotel, helipad, and parking structures were erected on the site thereafter. If I had to guess, I'd say that the "Cambridge" prefix would actually be a Waltham one, and represents a number transferred to the Canton facility when the one in Waltham was closed.
(BTW, Hank, did you know Bob Welch, who was president of BLH Electronics for quite a few years? I regret to note that he passed away on January 24th.)