If you could get a lighter 23" arrow and use a slight overdraw you'd be well up there in distance.
The complex primitive composite really does allow all the extras permitted back in the day as just regular flight allowances.
We really should be back over 500 yards in this class regularly.
Don Brown's unlimited record is well out there but there should be more shots filling that 350-600 yard gap, especially in more mortal draw weights.
From the USA rules;
"ix) RELEASE - Glove, tab, hook, rope, thumb ring, finger ring, non-adjustable hook and loop, and flipper are allowed for Primitive Complex Composite Bows. These items shall not be made from synthetic materials. Metal is allowed for a release aid. x) ARROW REST – An overdraw is allowed, not to exceed 4 inches (10.2 cm) in length, measured from the back of the bow to the terminal point of the rest. An elevated or collapsible arrow rest is allowed.