I cut, drilled, and tapped the manifold, as well as made a block off plate. I also have gasket material cut to fit the plate.

A friend of mine says the plate will never hold unless it's welded, so now i'm kind of worried.

I've been looking at different sealants, including j.b. weld, and high temp silicones but i'm not real sure what temperature that part of the exhaust manifold reaches?

Any ideas?

It is better to weld-on the plate if you can find someone who knows how to weld cast iron.

Exhaust manifolds can get up to 1400 degrees so JB Weld will not work.
For the "bolt down" plate, use high temp silicon sealer and "pile" a large bead of it behind the plate / gasket. Also apply the sealer to the screw threads.

If the surfaces are nice and flat, the bolt-on solution will hold but you may need to tighten the screw now and then.
DD

ok thanks.

Hopefully it'll hold long enough so i can drive to a place that can possibly weld or braze it.

You stand a much better chance of a good seal at this junction if you buy the good gasket for the "hotbox" area you're blocking off.

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Too many people who were born on third base actually believe they've hit a triple.

i found a boiler repair place, and a few other welders in my area. I'll call them in the morning and see if they'll do it. If not, i'll goop the hell out of it.

There are also good gaskets at www.remflex.com