grade indicates tensile strength...12.9 is equivalent to an SAE grade higher than 8, probably way higher than any bicycle needs.
You don't HAVE to use the 16mm bolts or even a 15mm unless you have some kind of fetish...as long as the threading matches and you have a washer or flange on the bolt, use what you have and what works with the socket you have.
I would NOT trust that any Co-Op has the Stronglight puller, the TA puller (23mm, NOT 23.15mm) is much more common and while it MIGHT work, it might also strip your vintage crank threads. Verify, verify, verify.