Transition-metal dichalcogenide (TMD) monolayers are direct-gap semiconductors with peculiar spin–valley coupling. Combining two different TMDs can lead to a type-II band alignment and formation of interlayer excitons (ILE). In MoSe₂–WSe₂ heterobilayers, optically bright ILE are only observable if the interlayer twist angle is close to 0° (aligned, R-type) or 60° (anti-aligned, H-type). Herein, low-temperature optical spectroscopy studies of these ILE in high magnetic fields are presented. Depending on interlayer twist, ILE transitions are either valley conserving or between different valleys. This allows engineering of the ILE g factor, changing its magnitude and even its sign. Additionally, applied magnetic fields induce a valley polarization of the ILE, and its buildup can directly be observed in helicity- and time-resolved photoluminescence, with peculiar features due to the dependence of ILE optical selection rules on interlayer registry. For both, R-type and H-type structures, it is found that at 24 Tesla, the valley polarization is resonantly enhanced, even though their g factors are markedly different. This observation hints at a scattering process involving single carriers within the ILE and zone-boundary acoustic phonons.