Total cross sectional area of 2.5" exhaust = ~4.9085".
Total cross sectional area of 2 1.25" pipes = ~2.45".
Total cross sectional area of 2 1.75" pipes = ~4.8104".
Total cross sectional area of 2 1.76" pipes = ~4.9087".

You see, just dividing in half isn't the answer. You will need 2 pipes of ~1.76" each, as 1.75" is still going to be too small. And that's if they are mandrel bent. If you are getting crush bent piping, then you will need a muffler shop that can estimate the inside diameter of their crush bent piping, and then calculate the cross sectional area.