I have two interfaces one with BNC wordclock and one with only SPDIF.
Can I take a cable out of the wordclock on one interface and plug it into the SPDIF on the other and they sync?
No that is not possible, you will need some device that can lock to wordclock and convert to spdif.
SPDIF will carry a Wordclock signal and in my experience you usually must use whatever interface that is connected via SPDIF cable, clock as the master clock to get them to sync properly. At least in my old set-up with a 828 MkII that is how I had to do it.
spdif is a notoriously bad transmitter and receiver of clock info and the specifications of spdif and wordclock differ so even if you do get it to work as Mandobilly64 suggests (and I’m not doubting it does work), it will probably suffer from horrendous jitter and miss reads.
That very well could be true. In my current set-up I do use SPDIF but only for in and out of a TC Electronics M300 effects unit, which it seems to do a good job for that, keeps the signal on the digital side there at least.