Holley 4557 spark control vent tube
 

So my LS6 does not have the TCS hooked up, currently I just have vacuum running from the base plate directly to the distributor. Looking at some pictures the TCS lines ran to the distributor, choke, and vent tube on the top of the carb at the secondaries. Car has been this way for a long time and runs well, so I am guessing the spark control vent is not necessary to run vacuum to? Was going to put the TCS back in since I have the original one that was removed back in the 70’s, but after reading more it appears to it’s more of a nuisance and will limit timing.

Spark control vent is just a vent, I believe it was vented to the top of the carb to ensure it wasn't open to elements. If not mistaken 71 and up has a small foam filter in the end of the solenoid VS the hose to the carb.

The vacuum break on the 71 kicks the throttle blades slightly open in 3rd and 4th in a coasting scenario and also limits full vacuum to the distributor after temp is up.