When I ran a carb on my SBC, the ecm was completely removed.
All the stock guages run independent of the ECM and do not need it for them to run. The 2 exceptions to this are the "shift" and "Check Engine" lights that are triggered via the ecm.
If you have an Automatic, you will need to use a pressure switch (or some other means) to lock up the torque converter.
The AC cystem will work just fine during normal opporation, but the ECM has a built in function to disable A/C at WOT if it happened to be on (avoids the power loss of AC at WOT). If you wanted to retain this fucntion you will need to wire up some other type switch (maybe based on engine vacuum).
[This message has been edited by fieroguru (edited 05-08-2010).]