Which pistons will you be using? With a forged, 4032 piston, I suggest .004-.006 piston to wall clearance for general nitrous use. Also, increase the piston pin to pin bore clearance to .0015-.0018, and gap the top ring .028, second ring .031 if they are ductile iron. A hypereutectic piston will need a couple thou more ring end gap. A forged 2618 piston will be similar to a 4032, but will need a bit more piston to wall clearance. A compression ratio of 10:1 works well for nitrous with premium pump fuel, up to about a 300 horse shot. A direct port system will give you the most control and versatility. I prefer to have dedicated fuel feed, and not use the fuel injectors for supplemental fuel. I also prefer a true timing retard, to limited advance. Do not port the 317 heads, unless you *really* know how to port those heads. What most people do to those heads ruins them. If possible, fit a 1.65 exhaust valve, and do the throat at 90-91%. A Ferrea 6000 valve with a radius margin is ideal for this application. The stock intake size is fine, just needs a good valve job. Watch the stem to guide clearance, especially on the exhaust. Strongly suggest no larger than a 1 3/4 inch header. For a cam, I really need all the vehicle info, but I think you will want something on a 118 lobe separation angle.