Radiator tank weld line uses 3.08 inch / 76mm width
There is now (2023 ) a lot of cheap insulators on the market out of China.. bloody hard to find quality.
This is the UPPER or Lower insulator that holds the Camaro (not Firebird TA) radiator into the top of the fan shroud and at the bottom in the craddles built into the radiator support panel. The Insulators fit into the shroud.
Fits but not limited to standard small block: