tm9-801.com

This is out of TM9-1827B 1 May 1944
Note that later remote mount hydrovac air cleaners were STAMPED with that information. Also note that even though the hydrovac air cleaner was moved to the firewall for series II vacs, the TM9-801 in 1944 is the only TM that shows it. The SNL shows the brake plumbing with the vac air cleaner attached to the vac.

Here is a later, stamped remote air cleaner for the Series II vac:
Roughly the same text, no decal.

For comparison, here is what's on my truck. This appears to the the air cleaner from the rear of the vac, just put in place of the actual remote mounted one:
I didn't see any markings.