For everybody waiting in breathless excitement for the end of the cake story, here's the finished product (the rest of you can look, too). After a couple of ingenious rounds of disaster repair, it ended up being pretty photogenic:
The cousins were fascinated by the fondant, and ate it (ewwwwwwwwww). My grandma thought it was perfect. My uncle said, "next time don't ruin my delicious cake with that disgusting frosting."
It was a good 50th anniversary party. We pretty much have the best grandparents in the world.