The Lyon and Healy Folk Harp uses Pedal gauge string, not folk gauge string. The bass wires are different from the pedal bass wires so you need to be careful when you order them that you get the correct ones, but the rest of the strings are standard pedal harp strings.
The Folk Harp is built so that you can string it with either gut or nylon as you please.
Mine also has a little bit of a bulge in the sound board. It is common on the Folk Harp. As long as it isn’t an extreme bulge it should not be a problem, although if you haven’t regulated the levers for a while you may need to in order for it to play in tune with the levers engaged (the bulge changes the length of the string slightly, and as a result the levers need to be adjusted for it to raise the pitch properly one half tone).
Switching the old strings off your pedal harp to your Folk Harp in this case will not hurt it (except the bass strings. Don’t put