After a long time of on-and-off looking, I may have found a 2010 Mac Pro with 2x2.93GHz Xeons, 2x5770s, a 512 gig SSD and what looks like 8x8GB of original Apple RAM as described on the back sticker.
Time to make a High Sierra flash drive using my 2017 MacBook.
Will keep you guys posted after I meet the seller and pick it up.
Well, I have the machine. It will need a very good cleaning. But... it looks like it will be a struggle getting an OS on it. Drive is wiped and I've probably made it worse doing stupid things in Disk Utility. High Sierra, which I have on a flash drive, won't install because it needs a firmware update it won't install. And my 12-inch MacBook doesn't want to make a flash drive from a Sierra installer.
Also annoying, the monitor I'm using doesn't display anything until the OS boots. This machine is running stock Apple GPUs so that can't be it. It's so weird - the same (sketchy) monitor, using its HDMI port and a DVI->HDMI, is able to display the boot screens on my MDD (unlike some other monitors that don't support Apple's older video modes, I guess), but it won't using a mini-DP to mini-DP on this thing. Grrrreat.
Trying to burn a Snow Leopard disk now