The northbridge and south bridge have been replaced by the IOH and ICH respectively on X58. For P67 the IOH and ICH are combined into a PCH, platform controller hub. All future Intel boards will have the PCh instead of the two parts, the main reason being that the PCi-E controller is in the CPU, which wasn't the case for X58.
BLCk = base clock its called the base clock because its the clock that the CPU, QPI, RAM, and UNCORE frequencies are derived from for X58, and some of those for P67.
HTT refers to AMD chips as the replacement for 'FSB' which has also partially moved to the CPU (CPU-NB). The CPU-NB on the AMD chips handle the memory controllers while the NB chip on the mainboard still handles the PCI lane and the SB controller.
The HTT (or FSB from a few years ago) represents the clock speed at which the controllers operate the CPU frequency and RAM. The NB also has a link (bridge if you will) to the SB which in turn communicates ports and channels and other functions with the CPU (HDD's, Sound, etc).