Non-uniform manufacturing variations and uneven usage wear and damage, referred to as mistuning, can drastically alter the dynamic response of Integrally Bladed Rotors (IBRs). Optical scanners, combined with Finite Element Model mesh metamorphosis algorithms, have provided capabilities to create analytical models that reduce the effect of geometrical uncertainties in numerical predictions. However, deviations in material properties cannot be obtained via optical scanning, so additional approaches are needed. A geometric mistuning Reduced-Order Model (ROM) is developed and modified to solve for unknown IBR sector eigenvalues that are linearly proportional to Elastic modulus. The developed approach accounts for both proportional and non-proportional mistuning and allows updating of the Elastic modulus for each sector in the ROM. Different tuned and mistuned modal reduction procedures are employed to understand the implications of each for identifying mistuning. Simulated test data with known inputs indicate the efficiency and accuracy of the method and improvements over using a traditional, tuned mode approach. The developed methods are then extended to bench-level traveling wave excitation data to discern how sector frequencies vary due to geometry and modulus mistuning.