Don't worry, I' ve done one of my friend's 71 Challenger, the car looked pretty straight but, as we were watching the sandblast process, we felt like crying.
There was so mutch Bondo on the car it was incredible, plus what had seemed like "not so bad" floors, finally ended up being nonexistent, in the end, we replaced rear left quarter, both rockers, both front fenders, floors, trunk floors, fraim rails, rear right wheel well and had to rebuild the firewall and front wheel wells.
The most important part is preparation, do one section at the time so, this way, you see results quicker and it builds your confidence, keep the pillars for last once your skills have been polished a bit.
Take your time and take it easy on the welds as you don't want to distort the surrounding areas and end up with an ill fitting car.
Keep the pics comming. Good work so far.