Clifford Gasket

Someone told me that I will need to order a gasket from Clifford to run a slant six Clifford intake/ header because its a much thicker gasket???

However I heard from another source that a standard fel-pro intake/ exhaust gasket will work just fine ???

which one is true ??

Can I use an over the parts counter fel-pro gasket or do I need to order one from Clifford ??