Why not? They were installed pretty much across the board in C10s due to vehicle gross weight classification. But to directly answer your question yes a 71 6cyl/3OOT truck would have had the TCS (or CEC) system.
Might want download a manual or two if you don't have them to more completely understand how your truck was built and what systems were used above the minimum required to run the engine.
An example of this would be if you have a functioning Neutral Safety Switch for you current trans installation.
* VIN/Model Decoders
* Power Team Charts (engine/transmission/gear ratio)
* Post Your Pickup SPID Blazer SPID Suburban/Panel SPID
* RTFM ... Read The Factory Manuals... download 'em here