As AmateurDragoneer pointed out I only like the variations of the GPA that begin 1.e4 c5 2.Nc3 d6.  After 1.e4 c5 2.Nc3 Nc6 3.f4 g6 4.Nf3 Bg7 5.Bb5 Nd4 is OK for Black if he knows what he's doing (of course it's playable for both sides).  White does have some other options after 2...Nc6, such as 3.Bb5!?, 3.g4!? (Martin recently wrote about this.), 3.Nge2,3.g3 (most of them aren't better than 3.f4 but a couple probably have more surprise value).  1.e4 c5 2.Nc3 g6 3.d4 Bg7 is a Modern Defence and 3...cxd4 4.Qxd4 might be considered to be also, but I haven't located any information on this exact position anywhere.  That was the main point of my post.  To be told specifically where I might find information on this position.  I looked in the Nunn/McNab Pirc and Modern book but didn't see it in there.

MNb, Glenn was saying that he only plays the GPA once black has committed to ...d6 so it is difficult for a GPA player because 3. f4 Nc6 4. Nf3 Bg7 and now 5. Bc4 (presumably what Glenn plays against 2...d6) 5...e6 and black can play ...d5 in one go.

This is a rather annoying move for a GPA player to have to face (at least for those of us who only play the GPA after 2...d6).  I was wondering how (After 1.e4 c5 2.Nc3 g6) 3.d4 cxd4 (3...Bg7 4.dxc5 Qa5 5.Bd2 Qxc5 6.Nd5 transposes to known theory) 4.Qxd4 Nf6 5.Bb5!? compares to the analogous position with the Knight on f3 (instead of Nc3 here).  One critical line would still be 5...a6 6.e5 axb5 7.exf6 e6 and now White has the possibility of 8.Nxb5 but that still doesn't look completely clear to me.  Does analysis exist on this variation somewhere or does anyone have any ideas on this?