The stock FI manifold on the early 280s is not a bad design and flows reasonably well with only minor mods(port matching). It only lacks and undersized plenum for high output turbo applications. One could easily have a shop chop off the backside of the plenum and increase the plenum volume for increased flow. And while the backside is off, you can do all the internal work needed to be done(polishing, smoothing, enlarging runners, etc.) Should be able to mod the manifold into a beast for under $250.