I have a GPSDO design I've been building and selling for a while now, and it's mostly successful, but sometimes the 3.3v buck converter to power the oscillator won't start up properly.
It isn't universal - most of them work, but it happens often enough that I think there must be some aspect of the datasheet that I am not heeding 100% that's causing the design to not be 100% stable.
When it doesn't work, the output is more like 1.7 volts instead of 3.3 volts. Momentarily shorting out the 10 µF cap on the input of the SC189Z is enough to get it to start up properly (but obviously that's a pretty heinous workaround).
The schematic is on the hackaday.io project page. The 2.2 µH inductors are Murata 1285AS-H-2R2MP2s (I couldn't handily obtain the part mentioned in the datasheet). The 10µF, 0.1µF and 0.01µF caps are ordinary X7R 0805 ceramic caps. The input power is a 6W rated wall-wart style 5VDC power supply. The OH300 requires 3W at startup reducing down to 1.1W steady-state (at 3.3V).
The relevant portion of the circuit starts with the buck converter, which is followed by an additional 2.2µH inductor and 10µF cap and 0.1µF cap as a ripple filter. From there, there's about a 1 inch long 32 mil wide trace over to the OCXO, where there's another 10µF filter cap, a 400Ω ferrite bead and a 0.01µF cap, then the power supply pin for the oscillator.