What is the best glue to repair the front heater box plastic?

I am going to need to replace my front heater core soon and I know two
of the bolt tabs that attach the heater assembly to the front body panel
are broken.I will try to glue and reinforce the tabs with the proper
plastic cement, whatever that is.If this is not possible I will try to
fabricate tabs from metal and attach them to the heater box with small
bolts, washers, and glue. I need a glue that binds well to the heater
box plastic and possibly to metal.

Now, to find that heater core…

Ed