I have some questions for you first...
Why are you looking to swap the 283 for a six?
Are you willing to rebuild an engine, or just find something that runs good and "drop it in"?
You say you want to stay with the stick shift. Do you want to stay with the column shift, or do you want to go to a floor shift?
You want to do 80 mph comfortably. This means gearing is going to be an issue. Either by using overdrive, or changing out the rearend to a lower gear ratio, or both. Your answer to question #2 will help determine this.
Are you planning on "hot rodding" the engine, or just running stock?
There are alot of little "gottcha" things that will need to be addressed, but which things, depends on your answers.
