My old SBC exhaust ran a stainless block off plate to make the manifold riser connection dry. It was 1/4" thick surrounded by a gasket on top and bottom. Water was routed from manifold to riser via external hose. Never had a problem. Other than the op having 3/4" more material, what's the difference?

http://i77.photobucket.com/albums/j7...imagejpg23.jpg