I have this tiny ASRock J3455B-ITX for testing. Cheap and slow, but Intel® Quad-Core Processor J3455 (up to 2.3 GHz)
J3455B-ITX (https://www.asrock.com/mb/Intel/J3455B-ITX/)
I might be easy to boot it from USB-stick for x64 tests.
Looks like it will take 2 * 8 gig modules of DDR3 of up to 1866 so it should run OK if the rest of it is set up right. My young brother is into tiny computers and he uses one of them to run his home entertainment setup. I gather the CPU is a type of Celeron.