Am I crazy for doing this on a 65 Barracuda ?

Other than the bondo issue there are other advantages to this preservation. Preserving the car is the main point and all else is gravy, as they say.
When I started I had this car sitting outside that ran and drove well but was deteriating. Previously before I owned it , it had the engine rebuilt at a technical college with the heads and valvetrain changed to run on unleaded gas. I don't know if they did the transmission or not.
It was sitting there with the top quarter trim clips rusted out leaving it bowed up and a total of about 20 clip holes allowing water to get into the body.

It had 2 holes where CB antennas were mounted at one time on the quarters . It had several small rusted out areas that water was getting into and it had pretty extensive damage at the bottom of one quarter panel. The amount of bondo I put in other than the quarter panel fix/experiment would equal approx the size and thickness of your phone. I think you could do this on a car with more damage and I wouldn't suggest making panels for large areas and if you have collision damage you probably need to address that at least to a stage where you can do a project similar to this.

I could have done things that just focused on preserving it but if I was going to do anything besides letting it sit there and rot , iI wanted to get more out of my efforts and see how nice I could get it look without getting into a long process and spending a lot of money on it . Since it was a preservation project I focused on keeping as much of the original metal in the car as I could . I doubt the car would ever have a market value that would come close to the money it would take to bring the car to the high end of it's market . A person could always do what they want in the future if they wanted to do anything differently .

I'm getting too long here, but want to explain my reasoning for choosing the methods I chose on this other than whether or not to use bondo so I'll probably talk on them too.