I have a few rally tunes shared for GT350R, one with stock engine one with Viper V10. Nice handling car in winter especially. Reasonably competitive, not OP though. Mustang DD can be quicker but 350 suits my style more.
It isn't a complex setup really if you know the general best guidelines. One thing I tend to do is soften the rear sway bar between 45-55 instead of maxing out at 65.