Attaching valley boards?

Thanks GBAR, helpful as always.
I've got a book that shows the framer putting the ridge in first and then butting the v.bs. next to the ridge. Does it make more sense to put the ridge on top of the v.b. and nail the ridge to the v.b.?

GBAR in WA said:

The nailing at perimeter line of valley over frame is critical and always on the engineering papers. e.g. 3"o.c. row at apex of valley board and 3" o.c. at old roof sheathing. (Positive tie shear-flow nailing). Be safe, G

Click to expand...

Let me get this right, 3" o.c. at the very highest point of both valley boards down the butt between the two valley boards into some structure in the house, correct? The ridge falls between two old rafters so I need to add a header between two old rafters so that I have something to tie into.
What does "3" o.c. at old roof sheathing" mean.

GBAR in WA said:

Ask me if you need some tricks for valley placement.

Click to expand...

I was going to run a chalk line from the heal of the ridge to the inside edge of the top plate to get my placement.
Any words of wisdom are greatly appreciated.

Edit: Also how far down the roof does the v.b. go? Correct me if I'm wrong but I think that it does not need to go all the way to the top plate.

Thanks GBAR,
Lots of detail here and took some concentration to picture it all.
One thing I can't wrap my head around is the flat 2x6 under the ridge. Could you explain?

GBAR in WA said:

After installing jacks with full support under by valley boards, install a 2x6 under the ridge, flat, sitting on v.b.'s for ridge support. Install 1x4's at every pair of jacks, to tie opposites.

Click to expand...

The 1x4's are rafter ties, correct?