dunno why he would use the 2.3 pal, but you need a sr20det tubular manifold, usually the cheap argos ones last on the sr20dets! the flanges line up just need cutting off and welding, there common one usually has to even runners going over the top, then 2 to the side

The best turbo to use would be a gt25-gt28 ebay turbo IMO, get the turbo elbow off a 200sx as that should fit on the sierra as it will be in the same position, ive worked on a s14a so if you need anythin give me a shout, the manifolds are everywhere lol