Non AC heater install help

[wpavlis]

So I have had my heater out for a while to fix the leaky heater core and to remove the sizable mouse nest within the inside section. I have the inside box restored and installed and tried to test fit the engine side box today. Does anyone have any tips for installing it? I squeezed and twisted it to get it into place, but every time the rubber seal arround the fan inlet would come off. I even glued it on using some weather strip glue I had. Maybe I need some stronger glue? If it matters it's a 68. I have the inner fender completely removed and I did not remove the hood hinge. Thanks!

Bill