I've seen at least three different options for using 3.3v oscillator modules on 5V boards, namely:
a couple of series diodes
a 47 ohm resistor
a proper 3.3v regulator.
The first two options work, but do have their own problems, so I will go with the third option of a 3.3v LDO reg.
I will use the LP2985 which is rated at 150mA so will cope with a TCXO and is readily available at Mouser.
And just in case anybody is wondering why not run the whole thing at 3.3v, the AD9850/51 is not specced to run at it's maximum possible osc speed at 3.3v.
While they do and are being run in that condition on the modules, current consumption and heat generation are increased markedly.