There are three blocks here which contain only 1 set of service buildings. I began to make these blocks after someone raised the question of how many houses could be served by one agora, one m.o., one theatre, etc...
Turn on the various overlays and watch the machine :)
76 House SSB
This block is wonderfully stable and is based on a design by Dodecahedron with a final key piece of info supplied by Nero Would. It is a figure 8. It is stretched to the max for loop size so the infirmary walker doesn't reach the southwest arm 14 houses. This does not affect block stability and the houses there will never get the plague since overall city health will remain perfect. Besides, people in the southwest aren't real hygienic anyways :)
92 House SSB
This is a monster and is too long a walk for the vendor to keep all the houses stable. Every walker does reach every house and every house can get to townhouse. (they just won't stay that way forever. It is a good example of walker directing and so I've posted it. It's fun to put on the overlays and watch the walkers go about their business.
86 House SSB
This is a shorter walk, more stable version of the 92 SSB. It is almost nearly, perfectly stable. You can tweak it and see if you can make it so. The houses on the top row fluctuate a lot but rarely lose their people and the northeast arm periodically loses actor access. Therefore it can be used in a city without screwing up your labor.