Ben, I've found if you use Permetex No. 3 (its a non-hardning, non-silicone sealent that you brush on) you shouldn't get any leaks - as long as you dont bash the seal in with a hammer. Use a peice of pipe the same Dia. to use as a drift to knock it in place.
With the Head Gasket, I use VHT copper coat (spray can) or Hylomar (spray can) - works really well.
With the other gaskets I use Permetex 'Ultra Blue' for things like sump/timing cover, & Permetex No.3 for the rocker cover.
As for the Manifold, dont use anything. Just put it on dry.