unless you have a mostly original car and even if you do I would just keep looking... bound to find one eventually for reasonable money.
This recent past get rich fever of ever one restoring their so called original cars is the root of the whole problem for our hobby including parts and restoration businesses. Most (99.8%) of these cars were at least street raced and beat hard and with so many restored cars out there being numbers correct matching or born with... not to mention all the fake tags, fake protect-o-plates, and fake paperwork, re-stamped blocks, re-stamped rears and re-stamped transmissions you really better be an expert on the Camaro or get an expert... even to verify a part...
IMHO the 480 looks original but the date code is not straight but that may still be original and the other one needs an expert eyes...
Back in the day the first thing many of us did was put on headers, take off the AIR system, replace the shifters, wheels, gears, etc,... all to go fast in a 1/4 mile!!! With so much fake crap from the crooks out their it has really polluted our hobby and I hope it has not affected the Chevy history... Thank God we have CRG and many good guys in the car hobby...