Winemaker, the objective was for the Max with MCAS to be sufficiently similar to the NG that differences training did not require the use of a simulator.
An issue with the modified Max is that MCAS.2 should shut down with malfunction, leaving the pilots with an aircraft which is different from the NG. Also, the Max may require specific procedures for recognising MCAS shut down, multiple systems alerts for an AoA failure, and revised instrument displays.
In addition it is possible that training for a trim system runaway, not associated with MCAS, will be required if the Max aerodynamics result in higher manual trim forces than the NG, or require quicker pilot recognition and action.
The NG simulator is not the same as the Max without MCAS, plus new alerting or switching logic. There would be significant changes and approvals required for an NG sim to be dual use.