Replace 1 7/8" pipes by 2 1/4" on a 6 cyl.

Looking under my car and taking a few measurements, I saw that I have a 2¼ O.D. front pipe. which narrows to 1 7/8 where the catalytic converter is welded. Could we start from the front pipe and continue this up to 2¼ all the way back?

Do you see any side effects to doing this? I would also remove the catalytic converter, (legal for such an old car where I live). Does this have any significant value?