I tried making my own Haunted Mansion plaque a year or two back. I tried to make it as accurate a replica as possible, but it didn't quite work out. My plaque is a few inches smaller than the actual ones. I had the exact measurements but not enough clay to sculpt it to that size.
I made a silicone mold and cast them in fiberglass resin. I was still not very experienced with mold making and I ended up destroying my mold after only getting two pulls off of it. :cry
But here is what I ended up getting.