The 737 actually has two fail operational autopilots (if you pay for it) and that of course enables CAT IIIb operation, same as for the small buses. You can of course order additionally a Head Up Guidance System but that is not a requirement, just another option and does not enable CAT IIIb on its own.
It is certified fully CAT IIIb for no DH and 75m RVR, our crews are getting the training currently (1 hour simulator practice) to be certified as well, until all crews are certified the operation is of course still limited to normal CAT IIIa rules, after that we can do as said above no DH/75m RVR on LAND3 and 50ft 125m on LAND 2 (special performance certification for LAND 2).