Phil Grable lives close to me and I've known him since 1960. We use to belong to the same archery club and I shot many tournaments with Phil and also hunted with him many times.
I also knew Dickie Roberts though he was not a friend as was Phil. Dickie took the Michigan State Field Archery Championship away from me in 1966. We were tied after the field and hunter rounds and Dickie shot a perfect animal round to beat me. He was the National Field Archery Champion at the time.
Dickie's "Fireball" bow that he made was a wood riser with a double hump in the limb. The bow you have is a Grable aluminum riser made by Phil and the limbs were made by Dickie who copied the Grable limbs. I know this because I just got off the phone with Phil. He told me Dickie copied his limbs and put his name on them and used the Grable risers. Phil said what you have is a "bastardized" bow...Phil's words..
Phil said it was probably made sometime in the 70's and it's hard to know how many he made, only Dickie would know that. I'd think it was a pretty rare bow and one worth hanging on to
Phil is 82 years old now and still hunts. I still have a bow that Phil gave me in the 60's. It's a prototype that Phil called a "One of a kind"