If the exhaust is done you could use a stock system from a 1981 Z28 - just install the pipe 42566 that is down stream from the cat flipped.
z28 exhaust With all stock parts it should not cost too much.
With all the parts you want to buy so far - have you priced them out yet?
I can't make any changes to the exhaust manifold at this point, because it requires swapping out the integrated cylinder head, manifold and carb in order to install the Langdon cast headers or Clifford shorty headers (their full length headers are for trucks and will not fit the ground clearance of a 2nd gen Camaro). I can't afford that for some time yet. So I have to use a single exhaust from the stock manifold on back to a single muffler and tailpipe. Reversing the Z28 splitter pipe wouldn't seem to fit that exhaust. Since the header pipe was cut, and everything is missing, I don't have to replace the catalytic converter. The shop near my house said they could build a 2.5" signal exhaust for less than $200. I'm not sure what other parts you are asking if I priced?
