offy 4 barrel with Dutra Duals question?

i need help getting my parts together.
I have set of Dutra Duals and an Offy 4 barrel coming in the mail

Will i need a block off plate for the hotbox on the exhaust manifold? Doesn't look like the two manifolds bolt together as do the super six manifolds

If i do need a block off plate, how thick can i go? there's an 1/8" thick one on ebay.

thanks so much.

God Bless

Keni

http://www.kenithomas.com