It's super easy in WA State. Send a registered letter to the last known address. Wait for it to be returned unopened. Go to the police station and show them the bike, so they can certify it exists, or whatever. Go to the Dept of Licensing and get an interim title.

This makes me the owner of the bike, with all the rights of the owner, for 2 years. If the ownership is not contested in that time, then I get the full title. If the ownership is contested, the "rightful" owner has to go through a dizzying array of hoops to prove that the bike is stolen... like filing a police report back in 2015 when it was last registered. (Its had 3 interim owners, two who have started the title-petition process, but never completed it.)

So it is safe to say the last title-holder has no interest in the vehicle, and it'll be uncontested.

But before I spend $600 powder coating the engine cases, and building a new under-seat gas tank, and boring out the cylinders and getting new pistons... well, I'm gonna do the due diligence first.

.... but paperwork just isn't as fun as wrenching on a motor! So I keep putting it off...