Throughout this thread, I've not heard one mention of any ownership papers or a simple bill of sale document. No papers to show your have any legal right to the motorcycle. If this is true, then the bike is not now, and never has been, yours.
Assuming you have NO papers to show you have any legal right to this property, and have paid no fees to the state for them to provide you ANY help... read on.
Cut your losses. Learn the lesson that a motor vehicle is not yours until the state says so, or until you can prove, in court, that you have a legal right to the property.
At this point, anything you do to create dual ownership papers, will be viewed as fraud and motor vehicle theft in the eyes of your home state government.
A mechanics lien will not be possible, since you do not have a signed paper authorizing you to provide work and service to the bike. You have no right for recompense for anything you volunteered to do on the bike. Particularly if you aren't paying for a business license, or have legitimate business papers and filing income reports on that business to the state.
So, you found a deal that seemed to good to be true. It was. It sounds insensitive, I know. But, you were paid for your time with the enjoyment of working on the bike, having no agreement beforehand either on paper or verbal, to improve what is legally owned by another individual.
If a person robs a bank and uses the money to garner investment interest, is he still entitled to the profits?
If the person in question was truly a total #$%*, instead of simply shady, he would simply call the cops and tell them he has located his stolen bike on your property. Would they assist him in recovering same?
Sorry, but just take this as a learning experience. Some lessons are learned the hard way. I've turned down many "good deals", because there weren't the required ownership papers. In the end, if people want to destroy their own property, they have the legal right to do so in any way that pleases them.
Who knows, maybe, just maybe, the guy will ultimately send future work your way when people learn of the nice work you did to his bike?
My $.02