I’ve had a car that qualified as classic – more German muscle than American, but the principles are probably the same…
Do you have a garage to store the car in?
Do you have a normal car to use on a daily basis?
Can you do bodywork yourself?
If any of the above 3 is no, then prepare to spend lots of money. The nice looking American muscle probably pre-dates galvanising and underbody streamlining/protecting. This means any water from the roads goes into lots of gaps in the car and just stays there starting rust pockets. If they are like classic Porsches, they probably rust from the inside out…
Fuel consumption you can probably control by choosing when and how to drive the car. Fixing bodywork, you can’t really control.
Buy it, but go into it with very open eyes about how much it will cost you. I wasn’t prepared for some of the costs, and it tainted my experience of owning what should have been the car of a lifetime (still had some damn good times in it though!)