Not understanding. Given the desired size of the side pieces and the size of the board, won't you have to be splitting it in two in any case? Why the glueing back together?. I'd say cut off enough of the big board to make the sides leaving a bit to allow for checks and other defects (maybe 38"), split that piece in half lengthwise, surface it as needed, and then cut the pieces to final size. You'll still have 6+ feet of the wide board left to drool over and you'll have your two sides.