My first magnum build, advice appreciated

I don't think Diablosport supports the Magnum engine trucks. SCT is the one you need like mullinax95 said. Hughes does not do their own tuning, they farm it out to a shop on the east coast. For these Magnum trucks, do a custom cam and keep your stock lifters, Hughes spring and retainer kit, and if the budget allows do the Hughes FI intake and headers. If keeping the stock intake, forget the spacers and fab or use a bottom plate like Dubob said. None of the bolt-ons alone will be magic, but Magnums respond well to cam, intake, and headers, and when keeping fuel injection an SCT tuner from someone good is required. The tuner also takes out some of the torque limitting programming.