Progressive 29.97fps to 23.976fps?

I'm encoding a concert DVD that was in 4:3 aspect ratio, but has thick black bars on top and bottom. I guess it's hard to compress cos it's kinda noisy, the original source was not very high bitrate (3 hours at only 7.8GB with LPCM audio). Also, lots of smoke and stuff floating around. Thanks Bach, I'll try your suggestion later.