Going Back to a 700R4

[jaredts]

I'm probably about to show my ignorance, which is o.k.  Isn't that the low vacuum switch which is required to disengage the lockup torque converter (under low vacuum) that you are trying to get working?  Also, isn't the knock sensor always in the block since it is essentially a microphone looking for a thud?  No vacuum hose on a knock sensor???

[Captkaos]

First off, an 85 C10 with a "H" 305 is the LE9.  It won't have a "ECM" under the dash, it has a ESC (Electronic Spark Control) which controls timing to the distributor. 
Depending on where the pictured Vac switch is located ( appears above the ESC locaton above the AC), it is the ESC Vacuum switch, and has nothing to do with the Transmission.

There is a another VAC switch just like this generally mounted to the booster bracket, it as jaredts pointed out is the low-vac switch so the converter will unlock in low vacuum situations.  There is also a brake cancel switch which unlocks the converter when you hit the brake pedal. 

Only on ECM 1987-up TBI motors is the control in the ECM and needs all the sensors you doesn't have and never had.

I am guessing you didn't take my suggestion and search for the answer.  I found these that directly address this:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=14209.0
http://forum.73-87chevytrucks.com/smforum/index.php/topic,7310.0.html
http://forum.73-87chevytrucks.com/smforum/index.php?topic=3925.0
http://forum.73-87chevytrucks.com/smforum/index.php/topic,21274.15.html
http://forum.73-87chevytrucks.com/smforum/index.php?topic=5947.0

[Grim 82]

I've been told by transmission shops before that they can set the trans up mechanically to lockup the converter so it wouldnt need any electrical wiring for it.

Yes. I had a 700r4 built with a hydraulic lockup. No wires, no vacuum, just the TV cable.