exhaust diameter help!

1974dodge said
i have a 225 /6 in it, stock. hopefully swapping to a 360 soon:p

The factory pipe size for the 225 /6 is: 1-3/4" headpipe , 1-7/8" tailpipe.
For 360 duals: 2" flange pipes, 2-1/4" intermediate pipes , 2-1/4" tailpipes.