I was wondering if a Ruger No.1 in 204 could be rebored to 350 Legend? If the reamer would not clean up the 204 chamber what would work?

.223 seems to be a popular rebore to 350 L. I don't know the answer to your first question.

If your original #1 .204 barrel is still in good shape, it would be an easy sell to the PD snipers. This would defray much of the cost to buy a new barrel of your choice, especially considering the cost of a re-bore & barrel fitting ain't free. Just a thought....

Good luck with your project.

or wait for the .400 Legend