Thick base gaskets for heat insulation. 
It also has the grommets so you do not crack the base as you tighten the carburetor down.  
You need a special gasket because this is for a high performance engine which can generate excessive heat that will upset the fuel/air mixture when you need it most.   

this carb can replace the OEM on the following: Ford, Mustang, Thunderbird, Lincoln, Mercury, Cougar, F150,E150,E250,F350,E350, and other Ford products.