I understand there are threads discussing evocations block as defensive rolls. This is a question on evocation blocks plus defensive rolls. 
In a sample on YS252 it mentions Harry putting up a power 5 block. The spirit blows through the block with a attack of 7, beating both Harry's block and normal defense and he takes 2 shifts of stress.
Two questions: 
1. Does this mean if you take down a block you also get your normal defensive roll? It sounds like yes from this example.  
2. When determining shifts of stress. Does a block stop any stress? So a 5 block vs 7 attack would have 2 shifts, or does the defensive roll determine the shifts of stress that land?
Having a block is like having two defenses.
Situation: I have a 5 shift block going on me and my Athletics is Good (+3).
Case 1:  Thug #1 tries to stab me with a knife and rolls Great (4).  I don't have to roll Athletics because the block protects me.  I can roll anyway (say I got a Superb, oh well, didn't matter).
Case 2:  Thug #2 tries to punch me in the face and rolls Superb (5), well that gets rid of my block, but I get to roll Athletics anyway.  Crap, I rolled Fair Athletics (-1 on 4dF).  Well, at least I had the block so they succeed with 0 effect since they got a Superb attack roll and I had a 5 shift block (I only take stress equal to the weapon rating, which is 0).  Without the block, I would've faced a 3 physical stress (Weapon:0 + 3 effect) instead of nothing.  So even though Thug #2 hits me, he doesn't hit me in a way that inflicts stress.
That is how blocks work.
In the example in the book, the spirit apparently is unarmed (Weapon:0) and since it got 7 (2 higher than the blocks shifts).