Heater Alignment and Acoustical Foam

[Wildergarten]

I'm planning my firewall layout as to where the electrical components will mount (see photoshopped layout).

There is a lovely wide open area on the engine side of the heater box where the electronic ignition module wants to be. I can mount it with studs welded to the wall so as not to interfere with the heater box, but I'd really rather tack in a bolt and offset the box with a layer of acoustical foam such as Dynamat. The problem might be alignment of the tubular "stack" on the heater box that goes up into the vent as to whether it will go in and pull down to an acceptable alignment once the heater box is bolted up against the foam.

Has anybody here tried this?