You might be able to get away with a normal open-ended wrench. If I recall rightly, the Swallow came with a difference shape wrench compared with the B17s... more like the traditional open-ended one, rather than a ring wrench with a gap to get it past the threaded shaft.

However, again from memory, the Swallow wrench has thin sides to it, and a normal wrench might not fit between the leather sides of the saddle.