Hi,
I have reinforced my stanchion bases by removing the bit of balsa core under the base edge (more on why later), then fixing it by using a combination of thickened Vinylester resin, fiberglass (1708 and 1808) and a G10 plate.
I say that because I used "A" in your picture, pretty successfully as a barberhauler with my 145% genoa although I think my track goes 6 to 9 inches farther forward than yours.
Dan Stone
Triple Play #9
The inner edge of the stanchion base is over the start of the balsa cored deck. Over time ('92 boat, 32 years old...), 4 of the 6 bases (and the bow pulpit too) cracked the top layer of fiberglass before I got the boat. I didn't realize this until I dried out core around it and it got wet again the next year.