The yanglou buildings of Quanzhou are composite architectural heritage shaped by overseas Chinese and local traditions whose front facades provide an observable interface for comparing local and foreign cultural combinations. As existing studies emphasize plan typology and lack quantitative facade comparison, this study takes 40 yanglou buildings built by overseas Chinese between the late Qing dynasty and the 1960s in urban Quanzhou, Jinjiang, Shishi, and Nan’an and constructs a workflow of data survey, acculturation quantification, stage identification, and discriminative contribution analysis. The results show marked heterogeneity: the veranda presents strong object culture expressions, the wall elements are dominated by subject culture, and the hierarchy in the composition is unstable. FCM results show that the facades approximate continuous transitions rather than a single linear sequence. PLSR results show that the subject and object culture proportions in the veranda and wall elements and the object and renewal culture proportions in their compositions contribute more discriminatively to stage identification. This study shows that Quanzhou yanglou buildings are not direct transplantations of Western styles but composite heritage grounded in subject culture, absorbing object culture features and generating only limited renewal culture, providing a quantitative framework for stage identification, value interpretation, and differentiated conservation.