mixing years

This is kind of parroting what has already been said. For classic muscle cars, I prefer correct looking. I am 100% OK with non-stock motor, tranny, shaved door handles, and other custom tweaks, etc. But for these cars I am not a big fan of mixing years. Older cars (like 49 Fords, 39 Plymouth, etc, are more of a blank canvas to me.
That being said, I TOTALLY agree that you should build your car however you want or need to. If you have a 69 Barracuda but prefer the 68 front end go for it. . Or if you cannot find or afford a 69 front end but found a more plentiful 67 or 68, then go for it. I do like the hood inserts on the 68 hoods. At the car show, I will notice the difference, but I would NEVER be so rude as to point it out to the owner. I ALWAYS talk to the owner about how cool the car is, the paint job, interior, etc. If he mentions the differences, then I will comment on them, but always in a positive way. I would NEVER slam anybody else's car in any way. That person is happy with and proud of their car; be happy with them.