The main files that I take along to dances are the ones whose names start with 'K'. The KR* files are "reel" sets; the KJ* files are "jigs". Most of these pages have a mixture of traditional contra tunes and klezmer tunes that have roughly the same feel. But there's really not much special about these sets, and you should mix them as you like. There's also a "KlezJam" set that is tunes from the two monthly Boston-area Klezmer Jam repertoire; these are still being tested at dances to see how well they work.
Let me know how it goes over with your dancers. My prediction: The stuffier fuddy-duddies in your crowd won't approve of using "strange" music for the dance. The rest will like anything as long as the tempo, beat and phrasing are right for the dance. But you should be aware that there's a very long tradition of using any music that fits for contras. There is also a tradition of complaining about "inappropriate" music. People have found 19th-century complaints about the use of polka tunes in contras, but now there are many polka tunes (mostly Irish) that are in the standard repertoire.
It turns out that there is much precedent for klezmer music in contras. In eastern European Jewish communities, the sher is the common term for a set of dances very similar to what is known in other countries as a quadrille or a square dance (though some shers are done in circles of couples). There are documents describing contra-like dances, too, either as longways sets or as circles of couples with a progression.
Also, an important part of the history of klezmer muscians has been playing for dances and other events in the larger Christian community. In much of central and eastern Europe, people have long had the attitude that the best dance musicians were either Jews or Gypsies. Part of the Jewish musician's job has been keeping up with the latest fashions in music, and providing dance music as needed. When a dance teacher came through teaching the latest dance craze (minuet or quadrille or waltz or polka or whatever), the klezmer musician would learn the music for the dance, and also adapt other tunes to fit. At several times in the past several centuries, the hot dance has been a form of contra, and there are relics of this scattered all over Europe.
It's easy to decide whether a tune will fit for contras:
48-bar tunes take a bit of modifying to fit, but they can work if you experiment with the repeat pattern a bit. One well-known tune like this is Yoshke (aka Ma Yofus; Tanz, Tanz, Yideleh; etc.), which has three 8-bar phrases. It's 24 bars without repeats and 48 bars with repeats. We've found that the patterns ABCB and AABBCCBB both work well for contras. Again, there is much precedent for arranging tunes like this. Some of the tunes in the standard contra repertoire, such as Scollay's Reel and Maggie Brown's Favorite Jig, were not 32-bar tunes originally, but have been modified to fit the dance.
I've been experimenting with a few tools to do useful things in
directories full of ABC tune files:
Man of the files here have names that include "_C" or "_B"; these are for C and Bb instruments, respectively. Of course, you can play them in whatever key you like, but the keys here are often the "standard" keys.