I asked SIF about No8 about 5 years ago, and the person I spoke to seemed competent technically? I have repaired plenty of exhaust manifolds with No8, and no comebacks so i guess it should be ok for stove?
All the SIF technical people had gone by then. Some of their more recent technical bulletins have been, shall we say, unusual. One gave the amps needed for a gas rod.
No8 melts at around 900 oC........not sure what temp a manifold gets to. I guess its less than that.