Stock '68 GTS 340" pinion angle question

That is an awesome diagram. I saw where some people on the forum said Doctor Diff was a good source of information. I emailed them earlier today and they said the same thing as you.
Just finished welding with the perches to the with it housing flipped 180°. Perches are perfectly level and I have 5° down angle, so when I flip it back the correct way, perches will be level and I'll have the 5° up angle as required.