First question is: what problem are you trying to fix? Does your
existing CU have rewireable fuses or cartridge fuses?

I do NOT have a problem. I just wish to upgrade from fuses to MCBs.
My fuses are rewireable types.

The pictures I've seen of MCBs seem to just clip onto a support bar and
have a screw terminal at each side for wires. If they screw to a buss
bar I'd only expect to see one screw terminal for the output to the
ring or spur or whatever.

Chris.

Chris.