What is a good 1960 to 1975, maybe a little more, era muscle car? I know the classics, Mustang, GTO and Challenger. Generally speaking, what is a good muscle car with a decent engine, handling, chassis, brakes, etc. Safest and most efficient one basically.
"...decent engine, handling, chassis, brakes, etc" None of them.
A new Honda Civic Si coupe will smoke any stoke traditional muscle car in any sort of race, expect maybe a straight line of a ½ mile or less. The new Si has 197 hp net by current measurement methods - that translates into about 300 hp by mid-1960's measurement methods.
On most of the traditional muscle cars, disk brakes were an option, or not even available. A new car will stop from 80mph in a bit over 200 ft. Traditional muscle cars required 300 ft or more.
Handling - dream on, a new sporty Corolla or Civic will pull well over 0.8g on a skid-pad. Even the best traditional muscle cars were at 0.7g, and typically around 0.6g.
Fuel economy - in a traditional muscle car, getting over 10 mpg was considered very good.
Just based on your question, there is no way you should drive a traditional muscle car, you would not be able to handle the lack of modern brakes, handling, efficiency, etc.
Avanti, Studebaker had a winner in that one.
This was in fact the first muscle car of the 60's that followed what would become known a the "Pony Car" class.
As usual Studebaker was just a few years early in the concept and paid the price.
I once owned a '69 Poniac Grand Prix. It had class and a really fast 428ci engine. It was fun to drive and had good brakes and steering.
Find one that is not worn out and you will be pleased.
I sold it and bought a '72 Olds family car for my wife and kids.