is there any real binifits of power to run true duals on my car its a 305 with hedman headers and i was ganna run the true duals in the stock locationright next to eachother but i dont wanna do it if im ganna be losing power and i dont want it to be to loud

If you are going to stick with your 305, I would just do a single 3" Cat-Back. You don't need a true dual.

if i did do it though would i be losing power or staying the same or gaining? as oposed to just having the hedman headers y pipe runing in the stock position with a cut out in place of the cae...the duals wouldnt have cats eather...and how loud will it be if i have that spiral cor muffler on the duals if i do that setup

I'm going to put headers on mine, with a cut-out before the cat. That way it stays legal and I'll just use the electric cut-out for more HP and sound.