dual valve springs are a must plus cheap and easy to mod the spring seat.for what you described the dual outlet ex manifold is all you need and the cam choice is determined by your rpm range.the ipd lifter and push rods are GM items which could be sourced locally to save the trip half around the globe.don't forget to check the piston deck height may need to plane the block to get the piston up to it's surface.there was a co. in Aust. who made manifolds for a single side draft carb for b20s .on a street engine may make more sense than two carbs. check Isky's site for there cam specs an have one ground locally or the b20e cam would work fine on you engine.