Maybe you should add some extra holes to increase the airflow for added
heat, if yours is inadequate now.  If you remove it completely, you may be
sorry later; it's probably there to add a needed restriction, or to stop
whistling sounds, or some other equally good reason.  Maybe it's part of a
hot-fotwell fix.  I've never heard of it or seen it in the manual; I've
never had my airbox out and apart (yet!).  I'd re-install it if I was in
your shoes; after all, it's such a PITA to get to it again.
  Anyone else care to add an explanation or recomendation?

Mike B.

But one of the puzzling items I found inside is a large plate that blocks
off airflow thru about 2/3 of the heater core. It is perforated with one row
of ~1/4" holes along the bottom edge, and three staggered rows of ~1/4"
holes across the top edge. Is this normal? it was sealed in, against the
core, as if it belonged there, but I have never heard mention of it. (And I
am one of those goofs who reads the Bentley for fun, just to see what is in
it, and what I will be in for, when a job comes due.)
>
>  Any clues? My heater never seemed very strong, maybe this is why? The
> only clues in the archives were some unanswered questions about this same
> item, from 2006, in an airbox transplant of a 1985 into an '80.