Yard Office...

Most likely, there would have been a yard office hear the throat of the yard, like where you indicated.  It very well could be two stories tall to allow the yard master to see more clearly what was going on out in the yard.  The lower level could have been used for crew facilities.  The only switch controls required in your example would have been for the turnouts involved with the main line and that would be done from a nearby interlocking tower.  Typically, the yardmaster has no involvement with the main.  His responsibility is the yard and union rules would dictate that access to the main be granted by someone else.  That is why there is a dedicated yard lead, so yard switching activities do not involve the mainline.  Switches in the yard would be hand thrown and track occupancy reported via telephones in the yard, or by documentation to the yard master.   A small yard might not require a tall yard office, but a larger, or longer yard would.  The layout I have been designing has a four track fiddle yard, but since it represents the end of a much longer and larger yard on the prototype, I am planning to replicate the two story yard office at the throat as on the prototype. 

yard tower

Thanks for the reply. I assume that a mechanical  interlocking with signals for the main and siding would work. I guess the tower could be used for a dual purpose yard and interlocking tower.

Probably two buildings...

If your trackplan is all there is regarding the mainline, I'd bet the switches involved with access to the main would be controlled from a different facility.  By the '50s, those switches could/would be controlled electrically from an interlocking, or junction, tower that is completely out of sight.  A prototype example I am aware of is the NKP RR in Toledo, OH.  There was a junction/interchange with the Michigan Central RR at the west end of NKP's Canal Boulevard yard.  The junction was controlled and signaled electrically from Gould Tower a full 2.5 miles away.  Gould Tower controlled the junctions of the Toledo Terminal RR, the Wabash RR, and the NKP RR at Gould, as well as the one between the MC and NKP.  This was in 1936 too.  I still think the yard office and an interlocking tower would not be in the same building.  If you want to model an interlocking tower with rodding, there is no reason not to do so with a seperate tower on the mainline side with additional rodding leading down the main to other signals or switches that are out of the scene. 

yard tower

I appreciate the detailed response. I believe I will locate the tower on the mainline side and add some signals for interest. The new tower could control the other end of the siding/main. I could simulate a electrically controlled system since I do not believe a mechanical system would extend to the far end of the siding.

Interlocking Rodding...

I have read that most interlocking rodding was limited to around 1,000 feet.  There was a lot of friction involved with the mechanicals and cold weather could make things even worse.  There was a reason that the levers in the tower were nearly five feet tall.  The operator needed all the leverage he could get to move linkages that had multiple bell cranks, and many rollers in long runs. 

Interlocking for yard office ....

As a telegrapher I often worked at Champaign Yard on the Illinois Central. We had an office in the yard office and had a remote control interlocking at Leverette Junction several miles north of the yard office. This inerlocking controlled a crossover for the double track as well as two yard leads for the north end of the large yard. 

Skip Luke