Ungapped ferrites have a very wide tolerance, so it’s true that AL won’t tell you much in terms of which material it is. Is the converter using current mode or voltage mode control? If you’re running voltage mode the core material could be important in that there is a phenomena called “flux walking/ flux doubling” associated with push-pull converters. Typically power ferrites flux densities are kept below .3 Tesla, but your push-pull is running in both directions, so voltage mode control total flux swing should probably be kept to around, or just below, that level.