Very simple, the 3rd number in the vin on a Camaro or Firebird will announce the engine being a 6 cylinder or a eight. 67 through 69 will be......

12337 for 6 cyl coupes
12437 for v8 coupes



12367 for 6 cyl convertibles
12467 for v8 convertibles

If you are looking at other years, let me know.