I would use no gaskets with a smear of silicon, as you did originally.
No gasket = no possibility of gasket blow out because there isn't one to blow out or leak!!
Some manufacturers, such as Chrysler, NEVER used exh a gasket to seal the exh manifold to the head. I had many of them & never had any problems.
With port matching the manifold to the heads, the port opening in the exh manifold should be a little larger all round than the port opening in the head, about 1/16". This helps reduce reversion.
Good luck.
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