Just want to know which head std has best flow due to casting shape valve type etc.

Are the T heads a factory casting from say a gli and have some port cleaning and larger valve's fitted and the "T" added or are they a different casting like larger port volume and shape.

I have heard that the AU T head is the choice head is this correct?
If this is correct is it because of the under cut valve stems or some other reasons.

Is there much of a difference with a AU GLI HEAD and a AU T head?

Which is the better head EF XR or AU GLI?
Could the AU GLI head flow better or equivilant to the EF XR if fitted with same size valve's and ports cleaned up?

Lots of questions there...

EB XR6 head is the best flowing factory head.

Although the AU's have thin valve stems and larger exhaust valves (e-series t heads also have 41mm valves), the ports are smaller than e-series so they dont flow as much as they could.

If your going to get the head worked it doesnt make much difference what you start with. You can take a stock e-series head, work it over, fit AU valves and it will flow just as much as an AU T head with the same work.

The best standard head is the eb head as Stockstandard said.