The increasing use of simplified Finite Element Models (SFEM) in early design phases requires robust and objective criteria to ensure their dynamic validity. While ECSS (European Cooperation for Space Standardization) standards provide well-established guidelines for test–analysis correlation, their application to the correlation and tuning of numerical models with different levels of fidelity remains limited. This becomes particularly relevant in modern digital engineering workflows, where several Finite Element Models must coexist and remain dynamically consistent throughout the project lifecycle. This work presents a practical framework for the dynamic correlation and tuning of Detailed FEMs (DFEM), Reduced FEMs (RFEM), and Simplified FEMs (SFEM), applied to the structural model of the E-Box for VenSpec-H Instrument, as part of the EnVision Mission (ESA). The objective is to achieve dynamic equivalence between models while preserving the computational efficiency required for rapid design iterations. The proposed approach combines classical ECSS-consistent criteria, such as eigenfrequency deviations and effective modal masses, with modal shape correlation metrics. In addition to the traditional Modal Assurance Criterion (MAC), a global indicator based on the symmetry of the MAC matrix, referred to as the MAC Asymmetry Index (MACAI), is used to assess overall modal consistency without explicit mode pairing. This allows distinguishing true dynamic discrepancies from simple mode permutations, which are common when comparing models of different fidelities. The framework is formulated around an iterative tuning process of the SFEM, in which selected structural parameters are adjusted to improve the dynamic correlation with a DFEM reference model. The methodology investigates the role of different validation criteria, including eigenfrequencies, effective modal masses, and modal correlation indicators, in assessing the dynamic equivalence between models of different fidelity. The proposed methodology extends the spirit of current ECSS validation practices towards multi-fidelity numerical model correlation, supporting the development of reliable digital structural models suitable for concurrent and early-phase spacecraft design.