@kithrup Send me an email to info@minifree.org and I'll sort you out. The T1650 is the machine that I recommend for your purposes.
The T1700 (haswell) is also compatible, using the 9020 MT image, but as I said that platform currently lacks ECC in coreboot's native raminit; ECC will work on the T1650 so it's what I recommend.
The T1650 is similar in size to the 9020 MT. Note that I sell the 9020 SFF. The MT is a micro ATX tower, and normal 1150 socket but takes Xeon processors with ECC support.