Given a finite dim rational homotopy type satisfying Poincaré duality, what is the best reference to when it is the rational homotopy type of a fin dim manifold?
It sounds like you are asking about the SullivanBarge Theorem. The original references are: J. Barge, Structures différentiables sur les types d'homotopie rationnelle simplement connexes, Ann. Sci. École Norm. Sup. (4) 9 (1976), no.4, 469–501. D. Sullivan, Infinitesimal computations in topology, Inst. Hautes Études Sci. Publ. Math. (1977), no.47, 269–331 (1978). You'll find a clean statement in Chapter 3 of this book, but to paraphrase: Suppose you have a simplyconnected Sullivan algebra whose cohomology $H^\ast$ is a Poincaré duality algebra of formal dimension $n$. Then it can be realised by a closed simplyconnected manifold if, and only if, one of the following holds:
In other words, the conditions which are necessary for realization by a smooth manifold are also sufficient. 

