Hi,

wrt locking DROs, I know that by tampering with the bias of the oscillator
transistor it is possible to pull the frequency a little bit (a few MHz
maximum at 10 GHz). Assuming that you can select from a number of DRO's,
find two that have the exact same (or near enough) frequency and try to
use them like this. The simplest form of tampering consists in changing
the supply voltage. The less simple one involves changes in the bias
circuit of the oscillator, but for the latter you need the schematics and
instruments. I do not know about the phase noise characteristics of
the DROs but I suspect that they are not very good. They should be
less good than a multiplier chain's followed by a DRO filter. Just an
opinion.

hope this helps,

        Peter