Bottom of A/C & Heater box

[MY6.2SS]

I was in the process of resealing my 84 SS box and noticed that the bottom part that is inside the car, has a crack in it.
I need to find a replacement. What year models will work and what engine size if that makes a difference. There is a 86 Grand Prix at
my local yard, it has a v6.

Thanks for your time and help, David

 

[85ss/85gn]

All the same 78-88 g-bodys

 

[MY6.2SS]

All the same 78-88 g-bodys

Thanks !!!