Trying to fasten a steel tube to an exhaust manifold

Does anyone have experience trying to fasten/connect a small diameter steel tube to a cast iron exhaust manifold?

I’m working on a 1979 Ford F-100 with a 300 CID/4.9L inline 6 engine. Part of the emissions system includes a steel tube that fits into a small, drilled hole on the exhaust manifold. The other end of that tube hooks up to a vacuum hose that then connects to a temperature sensor inside the air cleaner assembly. This is part of the control system for the flapper valve located in the air intake throat.

My problem is I can’t get the tube to stay in the hole in the exhaust manifold. As best as I can tell it is a press fit only – no threads, no fittings or clamping mechanism, etc. But while I can push the tube into the hole, it always falls out very easily.

I’ve looked at high temperature JB Weld, but I don’t think it will last on the high temperatures, an exhaust manifold can get to (500-1000 deg. F., as I understand).

So, are there any better ideas?

Thanks!