Heater core parts question

[Tachout]

On the way home from work today the truck started making a funny hissing noise. Then came the familliar sweet smell and I knew I had sprung a leak. I knew what it was before I even pulled open the hood. Heater core leaking right where it goes into the heater box. I knew it because it has been leaking a little but not more than a drip here and there. I have the heater core, and was just waiting to have a weekend off with good weather as it is not going to be a fast job, as I am sure I am going to want to clean and repaint while I am in there. I just looped one of the heater hoses back to the water pump and it is not leaking. I can get by for one day on the way to work and back.

Now for the question. I already have a heater core. Found a new one in stock at Autozone! I got a steal as they just wanted it off the shelf is what I was told. Now to my question. I went in to look at it this afternoon to see what it would take to get the core out. I noticed that the heater core is really loose in the box. I know that at one time this had to have a rubber gasket or something around the area where the heater core lines come out of the heater core box. I could not find a drawing of it, but did not spend a ton of time on it. I want to know what the part is called, and see if there is an exploded view of the assembly inside that box, as I have not had one of these apart before. I want to order the stuff that is inside that holds the heater core, and seals off the box from under the hood.

Any help would be appreciated.