Screech at 70mph.

He said the belts are not lined at all. It's the cheapest most obvious fix to line up the pullies that the fan belt rides on. I'm just not positive as why it only does it under load. Maybe it has a fan with a clutch in it that's going bad?
Pawned, let us know what you find that fixes it, or doesn't fix it.

OK I just now finished moving the alternator 1/2" forward on the engine. I personally do not think this did it, but IT HAD TO BE DONE anyways.

Could even just be the wind over the body whistling, and that would explain the only at 70 part.
No, but I did hear a rattle when the car go on the freeway, that turned out to be the wiring to the front marker light. I had not secured the wiring after painting.

I am still very suspicious of the carburetor. But then again, lining up the belts may have done it.
I will take it out in a few hours. Need to rest up for a while. this COPD is kicking my butt the last couple days