Peter the Boss 351 crankshaft damper is a collector's item, worth more than $1000 USD, highly sought by someone restoring a Boss 351 Mustang. So they are over-priced. The ring was made of iron, and the hub was made of nodular iron. They are also 45 years old, the rubber isolation ring shall not be as resilient as it was when it was new, so the damper will not perform as well as it should.
You can acquire a new damper made 100% of steel that performs as well as the Boss damper did when it was new, and save money. Steel is heavier and tougher than iron. Something to consider.