Use a RemFlex gasket. Have the manifolds machined flat while they are bolted together to eliminate any warp. The gasket between the intake and exhaust at the heat riser needs to be replaced anyway, so they should be separated and checked for warp individually. Were the alignment rings used between the intake and the head? They ARE NOT optional.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!