I would solder it because you could always do the other if it doesn’t work out. Mine looks like someone re-soldered it and I’ve thought about neatening it up – but it’s holding so I don’t know. It also has a drain valve (like one of those T valves on a radiator) inline with compression fittings between the ballcock and the carb to drain the tank and carb bowl. It’s old but I suspect that it’s not original to the motor. I find it more convenient than the drain screw so that may be something to consider.
The drain valve, the re-soldered joint, spark plug wires, condensers and the rubber tiller grip are really the only things I suspect are not original to the 1930 K50. The grip is from an Elgin but I’m thinking Elgin bicycle – not outboard. I may try to find a correct replacement. Sorry for the long answer but I’m also just days away from trying it on the water so I’m stoked.