Replacement engine followed very quickly by new heads is a major concern. I doubt you will get the truth but it does suggest it might be a quick offload by the previous owner due to ongoing issues.
A common issue with the V8 is exhaust manifold leaks which sound just like something tapping - an issue I had with my own RRC after doing the heads & a cam & followers replacement. Immediate on startup & caused our cats to learn some interesting new words. I had a suspicion it might happen as the exhaust manifold faces were quite badly pitted & the new gaskets couldn't take it up. Refaced the manifolds & all was well. For the curious these were SS tubular manifolds fitted new some years previously & the rust pitting was appalling. The heads were unmarked.
A common issue with the V8 is exhaust manifold leaks which sound just like something tapping - an issue I had with my own RRC after doing the heads & a cam & followers replacement. Immediate on startup & caused our cats to learn some interesting new words. I had a suspicion it might happen as the exhaust manifold faces were quite badly pitted & the new gaskets couldn't take it up. Refaced the manifolds & all was well. For the curious these were SS tubular manifolds fitted new some years previously & the rust pitting was appalling. The heads were unmarked.