Try clamping off the air bypass hose at the back of the plenum chamber,with the engine hot and all loads off,(in neutral,A/C off etc) it should still idle at 450-500 rpm.This is the base idle setting which has an effect on the slow running qualities of the engine.(Keeps the idle stepper motor in its correct range of operation to respond to demands of load or throttle position)
If the motor stalls when you clamp the pipe off you adjust the base idle using the screw on the throttle body under a little alloy core plug close to the throttle butterfly shaft,core plug is about 12mm in dia - dig it out with a hammer and sharp screwdriver if its still there.
This is not a cure all - it is another piece of the set towards making a v8 run as it should.Hope it helps