the 90+ manifolds do not have the spreading problem at the flanges like the early design does, because the flanges are tied together. But the flanges can and do warp out of flat.

The flatness has to be checked and restored...if you don't want to have to replace flange gaskets every month.

Another reason for wanting the flanges to be flat: to reduce or eliminate any stresses that unevenness at the flanges might induce on the runners...twisting the runners and contributing to cracking or more cracking. This manifold already has two cracks. I would much prefer that those cracks not become larger.