The recipe I followed replaced entries 11, 14 and 15 in the vector table.
Below is a snippet of mk20dx128.c where some of my defines are shown...
fault_isr, // 9 --
fault_isr, // 10 --
#ifdef TEENSY_USE_FREERTOS
vPortSVCHandler, // 11 ARM: Supervisor call (SVCall)
#else...