My '72 Grandville has 71-80 firebird headers on it. The right side is a perfect fit. The driver'* side required a 10-minute cut-and-past MIG weld of the shift arm to rotate it 180 degrees and thereafter worked perfectly.
Make sure the trans crossmember has a hump on each side of the trans mount, or you're going to have trouble with the passenger side header. Most do, but some do not.