Dan,
I know that poplar in recent years has become popular
as the wood of choice for trim. It's a fast growing wood that mills and finishes well and since trim is almost always painted now instead of stained, the woods normal colors which include an ugly green, at least on the east coast varieties, are not an issue. I knew a man in Virginia who had 40 acres of mostly poplar and a mill who built his home out of it, contrary to the local 'experts' opinions it has held up well for decades in high heat, high humidity conditions. Your using poplar on the combine in the perpetual toaster oven will be a testament to its durability.