cl,
you typically find these long rods anchored in the bottom spider/ spreader plate of the filter and then the manifold is held down by 2 wing nuts at the other end. i have several pairs of these for the 48 sq ft filters. the Pentair part # is V38-108 and they are 27.5" long. $30 each rod, $50 for a pair... the stainless nuts are an additional $5
have them for the 60 sq ft filter. the pentair part # is 59002700 and they are 33.5" long.
have tie rods for hayward filters as well and have the spider bottom plates (pentair part #59000500) as well