is there some special places the bungs should be placed ?
There is nothing you should need the egt probe or afr meter for unless you are attempting your own calibration.
The ecu in your car is equipped with the ability to monitor both parameters and to adjust the engine operation based on the results of sensor feedback.
EGT's are important if you have calibrated your ecu beyond its ability to properly model them itself which is very rare. If you are deviating from a standard tuner and getting into some "custom" tune that turns off some of the ecu's safety features it may be useful as well.
AFR is only important if you expect that your fueling system is prone to failure and you want to try and save your car when a part fails like in Nitrous Oxide systems. Again, the ecu will be able to monitor afr and adjust it as needed.
However, if you still want to use these gauges, both should be placed as close to the combustion chamber as possible in order to get accurate readings. The EGT probe is best inserted directly into the turbocharger connection flange to the exhaust manifold so you measure pre-turbine egt's. The afr gauge is best placed as near the turbo exit as possible and should be the first bung from the turbo on the downpipe that will fit.
