I've decided to modify the design to use the TM4C1294 series MCU.  It has essentially the same feature as the MSP432, but with a higher clock speed and it is currently in-stock at multiple suppliers.

The CPU clock speed is nominally rated for 120MHz, but I have so far seen no issues overclocking it to 125 MHz to get a clean 8ns of timer resolution.  The 32-bit timers also seem to have no issue operating at 125 MHz.

I've added an e-ink display to the design for debug and status purposes, and also implemented DHCP and NTP.

I've been using an EK-TM4C1294XL eval board for prototyping. I'm currently working on an eval board layout for the DCXO and temperature sensor.  The GPS eval board should be arriving sometime next week.