Mopar M1 Manifold Injector Bosses, Not Drilled Out

If your manifold doesn't have bosses cast-in, you could use a similar jig for alignment to drill the holes in your manifold's runner, making it ready to weld in a pre-made bung like this one.

Injector Boss - Weld In - Aluminium - Large

You would need to use a large end-mill instead of a drill bit though. And you'd need a kegger manifold to use to make the jig.