will the sissybar from a 99 savage fit a 05 S40 with out any mods

You also need to swap the bolts over. The 99 is held on by four bolts on each side, whilst the 05 the three bolts and a pin/grommet locating arrangement. This is no problem to swap over, but because the 05 bars are about 5mm wider, the bolts are longer.

I have just finished doing a swap the other way around. I fitted the 05 bars to my 98, as I didn't want a sissy bar on mine.

Takes about 1 & 1/2 hours to do, including swapping the helmet locks and indicators over, as they're slightly different too.