I'm replacing my heater core and purchased the heater box/core gasket set from one of our restoration companies. I didnt receive any instructions for the 10 gaskets that come in the bag. I called the parts company and was told that they dont have a diagram nor did he have any ideas at all about installation, where, or if I needed all 10 gaskets. (Oh non AC)
Now yes a couple maybe a few gaskets are just plain as day where they go. Does anybody happen to have a diagram/instructions for the gasket set? Or any feedback on your installation of the gaskets whether you used all 10 or less would be appreciated. Thanks Johnny.

I just remember that I ended up putting gaskets on all the interior "flapper" doors even though there was no real evidence that any of those doors had ever had gaskets on them.

And there is no "gasket" for the inner and outer "suitcase" boxes to mount them to the firewall. Instead, the factory used 3M strip caulk or "dum-dum".

I used strip calk on the outer firewall one and i put in new jute padding under dash and it appears that it goes between heater box and firewall so that was my gasket on the inside. Be forewarned getting it all back in with the heater core and everything else was a major PITA!

Interesting, just got done replacing my Heater Core and the inner box (as inside the car) had a factory rubber gasket that was used against the firewall. I reused it because it was in good shape. Please note this is for a AC car. On the outside it was dum-dum.