I actually used the heater plate itself. On the inside I welded a round piece of steel, painted the whole thing black & bolted it back in.I found it easier to make your own.....thie is on my 71 DUster.
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This was my first attempt...it was a plastic that ended up warping. I have since made a metal one and painted it wrinkle black....
I'll see if I can find a picture. here it is....
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Used the pattern from the heater plate.
Aloha Mike