Stooby, yes, there are seals that are missing. Basically, large wide rubber bands! One between blower housing and heater box, and a narrower one between the blower and kick panel.

https://www.americanclassic.com/1955-59-Deluxe-Heater-Bands/productinfo/68%2D701/

Nice album and details, Flxible!

Mike
1955 Chevy 6400 ex-flatbed (no bed now!) sold September 2023
In the Stovebolt Gallery
1958 Chevy 6400 flatbed W/dump
In the Stovebolt Gallery
1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
In the Stovebolt Gallery

Sufficient unto the day is the evil thereof