Banjo tends to be more part of Dixieland or of traditional New Orleans Jazz than guitar--My guess is that you'd like you'd to play the older novelty stuff and standards, and there are several guitar styles that you can draw from: Django-Hot Club sort of stuff, Nick Lucas type chord melody stuff(a la Tiptoe thru the Tulips), the Eddie Lang/Joe Venuti sort of stuff, and the Dick McDonough/Carl Kress duets, which laid out they way that guitarists played forever after--

The key to all this stuff is to simply work out of a chord/melody lead, played over solid rhythm guitar, playing whatever dance beat is appropriate to the tune your doing--You then can break into any type of part that you want at the appropriate place in the tune--

It is often appropriate to use some sort of moving bass line as part of the rhythm--often moving the way that Frank describes the trombone part--you can give this part to a third guitarist-

With three guitars, you can also have the lead play the clarinet obligato(again, as per Frank, above)--one of the guitars can also play the chord blocks that horns would play--

When you work with a guitar duet or trio, it is often helpful to cover the lead with an electric guitar and the rhythm with an acoustic guitar--

Also note that, as daunting as Django's solo style may seem, the real trick to making the music work is in getting the rhythm guitar part right,It generally was generally played by the frequently overlooked Joseph Reinhardt--