VPX, thank you for your email. I have successfully re-encoded video to 720p mpeg1 using FFMPEG and your requested bitrate/framerate. The way you do it using Vegas is the following. You follow my tutorial here (you will have to adjust the project settings according to your own source material though, as you normally do):
and then you save it on that same folder discussed on step 4. Then, you run that .bat file you just created by double-clicking it, a DOS window will open and it will start re-encoding your video to 720p mpeg1. Enjoy!
One thing though, mp2 does not have good audio quality so you might want to up the audio bitrate from 96k to 128k in the script. I leave that up to you.