Re: Keel Bolts
There's no point in opening up the keel proper to inspect the bolts there - they will be perfect. The only place they deteriorate is above the keel, either where they go through the hull (most common) or where they are visible in the bilge (obvious).
If you cleaned out the ply and replaced it with solid glass and saw no signs of deterioration, I agree with the others - don't bother putting new ones in.
If you still want to do it, your plan is good but I'd go even deeper into the lead if possible - 9" is pretty shallow in a lead keel.
I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.