Since people wanted to see how it turned out. This is a 330x330 object that covers the entire purported print area of my machine.
I'm ashamed to admit that I undershot my filament usage calculation slightly, and I chickened out just before the finish line. I didn't have any more white in stock, so I switched to some grey of the same type from the same manufacturer by doing a mid-air refuel, shoving the end of the new spool in chasing behind the very tail of the old one. I don't think it looks too bad. I may just spraypaint the entire thing white later anyhow. I wanted to use a light color in order to more easily spot and keep track of screws and springs and such.
WOW! That is super even. I looked at mine with a FLIR attached to my phone, and it had definite hot spots. It might be time for a new heat bed.