There have been other threads about the Custom Autosound Radios. I have a USA-1 in another vehicle, it fits, looks like a bad copy of a stock unit, and the sound quality sucks, IMO.
If your dash is already cut up and you aren't doing a "restoration" I would just enlarge it to fit whatever modern radio you prefer.
Other option is a hidden radio, like in the glove box.
Here are some links:
http://67-72chevytrucks.com/vboard/s...ighlight=usa-1
http://67-72chevytrucks.com/vboard/s...ighlight=usa-1
http://67-72chevytrucks.com/vboard/s...ighlight=usa-1
http://67-72chevytrucks.com/vboard/s...d.php?t=404555
http://67-72chevytrucks.com/vboard/s...ighlight=usa-1