This is how I blast frames. It's an HF pot blaster and I use Black Diamond media.
This one is my '55 Bel Air frame. I just flipped it over so it's about 3/4 done here:
Here's my '57 3200 frame with just a little more needed to finish it off:
Here's the cab bottom after I just finished blasting it:
The Black Diamond leaves a perfect profile for epoxy primer:
I generally do not wholesale blast outer body panels. I strip with a D/A using 80 grit or use a stripping disc on a 4 1/2" angle grinder. Then I blast what the D/A or stripping disc cannot reach or is just impractical to use like the firewall, door jambs and cab interior.