Used trucks from the southwest sell at a premium here because they aren't rusted to death, you've never seen what salt does if you think it's the same. The calipers are full of fluid, if you're swapping the lines your air bubble is right there where you broke the line, aka on the steel block in front of the hose. Bleeding them at the hose connection is past the air bubble, completely fine. The bleeder is better obviously but in reality the caliper is completely full already, you are simply bleeding the connection you broke open, and you are doing it under pressure. If the brakes are firm you're good, if they're soft you have air in there. If you did the hose its a bit tougher, but still possible. You can bleed as much as possible at the hose connection to fill the hose, pull the caliper loose and compress it, which shoves all the fluid (and the tiny air bubble) back in the line, and then bleed it again which clears the air. It's an air bubble guys, not a big deal to outsmart the engineer who didn't account for rust.
