Heater Cover/Plate on Firewall

AndyF makes one. See here.

I got a repro plastic one off Ebay before AR Engr. started making them. The one I got wasn't made well at all, it was rough and porous. I may get the AR one anyway to save myself the trouble of fixing the other one.

You could also make one fairly easily. Its just a round, flat piece of material with 4 holes in it and one flat side.