1. The 451 KTu is the MOH unit, but it cannot be used in a 551 KSU. It does not work the way you imagine.
2. The loop-thru method means that the 5 rows of output pins can be used to terminate one double-ended (female/female) station cable, with the wires punched down using the "other end" of the punch-down tool. (the blade can be reversed in the handle to allow a wire to be terminated and then head off to other points, without cutting it off). It assumes that one, double-ended cable can be run to two (exactly the right) locations in a wiring plan, with no slack, and look like someone sane did it. This method assumes ten stations, two at a time, at the opposite ends of 5 cables.
This suggested cabling method ranks among what is one of the stupidest suggestions ever found in a Bell System practice. Don't even think of doing it that way. Use one 25-pair stub cable, cut down in the KSU, and terminate it on a 66B25 block, outside the KSU. Then terminate your station cables, two per block, on 66M50 blocks. Run cross-connections from the feed block to the station blocks. That will allow you to energize ten stations.
The shoebox cabinet is just too small to do any neat wiring work inside, unless you are just using it for a demo, feeding one or two phones.
