Two From 3's Bricked - SWAPPING PARTS HELP

I have an older one with a mad bed tentioner motor, and a newer 3+ that just fails to initialize. I’ve been through support on both, opened them up, checked cables, cleaned out, lubed up, hard reset, you name it nothing helps.

It stands to reason I have 2 identical machines with 90% functional hardware, so I should be able to Frankenstein them together for one usable machine, yes?

Would it be easier to swap tentioner motors or mainboards? I’m mechanically inclined, not worried to try any of it. Just curious if anyone has any experience doing exactly this swap out?