| I was in the exact same situation as you a few years ago. If you already have jazz chops on the mighty electric thunder machine, I'd go grab yourself a bass, a bow, a copy of Simandl book 1, and a teacher. Learning classical bass technique will give you the necessary left hand chops for the jazz band while you're at it, and just sit down with a good jazzer once or twice and have them teach you proper jazz pizz technique. You should be good. Just be careful, in switching from electric to upright, that you don't hurt yourself when you're starting out, because if you start to practice a lot and you still slip back into bass guitar flat finger technique when you're learning, you most likely will get some godawful tendonitis. When you start out be really aware of your left hand shape and make sure you always keep the fingers arched and fingertips on the string. And if you can, learn on a set of light strings, like Corellis, it'll help keep you from hurting yourself while you build up the strength in the LH.
__________________
"I know, sir, that I have played out of tune, but once I learn where to place my fingers, this will no longer happen." - Giovanni Bottesini, on botching his conservatory audition.
| 
