289 improvement ideas

the stock heads an handle a decent amount of power, though at some point they do become a restriction. that said a 4V carb upgrade, use the performer rpm or weiand stealth intake manifold and a 600 cfm carb, i prefer the edelbrock 1406, but there are a number of good carbs out there to use.

dual exhaust is great, add a set of tri-y headers to round out the exhaust, they are designed to operate in the mid ranges and will add power to the engine.

for a cam upgrade, look at cams that operate in the 1000-5000 rpm range. that is where your engine will operate about 80% of the time.

remember shelby used the stock heads on the GT-350s, even the race cars, though he did port them for racing, and the shelbys dominated their class in SCCA racing, sometimes even beating A production cobras. so since oyu are not going to make around 400hp, your stock heads will do just fine.

i havent put my tri-ys in yet, but i think they will fit better than the 4-1 tubes i had in the car, and they fit pretty well. as for your not so smooth idle, you might have a vacuum leak in the stock engine, rather common issue as the intake gets a bit loose over time. i have had that happen a few times over the years. it stopped when i went with fords suggestion of torquing the intake to 30ft/lbs, and changing the pattern i used to torque the intake down, starting with the four corners in a criss cross pattern, then using the stock ford pattern to torque the intake down. that prevents the inner bolts from loosening up when the outer bots get torqued down.

the cam manufacturers tend to be conservative when recommending cams, personally i would go with either the 260h or the 268h grind. i think for your application the 260h would do you just fine. the 252h is perhaps a tiny bit better than stock.

then the 260h cam is for you. the 268h idle tends to be a bit lumpy, but then it was designed that way, and still give good mid range power.