Since those split exhaust manifolds aren't connected in the center, using a blind pin at both ends instead of bolting them probably isn't necessary. If you convert back to a single piece manifold with a heat riser, definitely don't bolt the ends down. Those end holes are larger than the alignment stud by quite a bit to allow for heat expansion of a long single piece exhaust manifold. Bolting the ends down can, and usually does end up with a cracked manifold.
Jerry
