The underlying rationale for performance increases from each of these parts is "breathing". Both parts enable the engine to "inhale" more air/fuel mixture. With that in mind, if you add a supercharger to stock heads, stock cam, you are restricting the supercharger to less than its capability. While you might geneated "boost" through the supercharger, the air it is capable of "pushing" under boost through your carb/intake/heads/exhaust, is choked off , and restricted factory intake . The general rule is that a supercharger running say 6 pounds of boost will increase your non-boost, rear wheel hp by around 40%. (conservatively). Thus, a stock 302/2v combination with a factory cam (circa 1970) is factory rated at the flywheel at 210 hp. 40% of that is 84 hp.
For maximum performance from your supercharger, you need to build the engine so it makes peak hp/torque in its naturally aspirated configuration. This means you open up everything that allows the engine to breath - carb, intake, heads, and exhaust. For example, the Edelbrock performer rpm total power package for the 302 (this is intake, cam, heads then add a 600 cfm carb to it, then also add dual exhuast and headers) is dyno rated by Edelbrock at 346 hp (I only got 253 at the rear wheels - dyno'd - with this package!). 40% of 346 is 136 hp! compare that to the 84 hp!. Same supercharger, same level of boost, but you are getting about 50 hp more, just because you built the engine correctly.
Also, for best use of a supercharger, you need to have a compression ration of no more than 8.5:1, 8:1 is even better. This is because the addition of boost has the effect of increasing your compression ratio. If you add 9 pounds of boost to a 9.5:1 engine, your compression ratio is so high you can't run pump gas! I think the effective compression ratio is something like 18:1. Not good.
Thus, if you are going to run a supercharged application, make a purpose built engine for it. This means you have larger combustion chambers in the head (I think AFR offers 58 or 60, but if they have 62 cc, I would take that), then don't mill the head or otherwise raise the deck height. Run flat top or dished pistons, which increased the combustion chamber size. Use a cam with a long, split duration cam and get lots of lift (.545 intake/.560 exhaust or above), but a tight lobe separation 108 or 110.
You should use forged pistons, forged connection rods, and a girdle on your main caps, plus ARP fasterners, even studs if you want to get a little more bullet proof on the bottom end. If you are running 9 pounds or more of boost I would get O-ringed heads and use the wire-lock head gaskets. Your rings should be purpose designed for forced induction - some say ductile iron top ring then the more exotic for the scraper and oil rings.
With a carb, you have to consider implosion proof floats and a special type of power valve. Without hte implosion proof floats, it is possible, at least in theory, that boost will collapse the stock-style floats.
The two most dangerous things you can do when supercharger is to run too much timing advance and/or too little fuel (lean). Thus, you would probably want to change your carb to something like a 750 and then back off your total timing to around 32 degrees and then back off your static, or intial, timing by 2 degrees.
Lastly, not all superchargers are the same. You have the the centrifugal type - like vortech, paxton, procharger - and then you have the roots style (I lump the twin screw type superchargers into the roots category). The most common on the old stangs are the centrifugals. Kenne Bell makes a great roots style supercharger, but only for fuel injection applications. Holley, through its Weiand line of parts, makes a great roots style supercharger, but again that is only with fuel injection.
The two styles of superchargers differ significantly in where they produce their boost. The centrifugal superchargers require the revolutions of the supercharger to increase in order to increase boost. Generally, you will not achieve full boost on a centrifugal supercharger until you are in the 5,000 rpm range or more. In contrast, the roots style supercharger makes it full boost down low - 2800 rpm, and it keeps at the peak for a broad rpm range. What this means is that the centrifugal supercharger as a relatively narrow peak boost range, measured against rpm, and I call it "spikey" for that reason. In contrast, the roots style supercharger has a broader rpm range of peak boost, or in other words, has a flatter peak hp curve.
As you can see, the starting point is to build your engine the best you can, without the supercharger, then tweak it when you add the supercharger by adding more fuel - through a bigger carb and upgraded fuel pump, and then change the cam when you add the supercharger. AFR has a 185 or 205 head for the 302 that would be happy with a supercharger. I think their 165 would be too restricted and even the 185 might be a tad less in flow that the supercharger would be best with. I am sure the 185 would work, but not as well as the 205.
Well, here are some things to think about. Just my 2 cents worth. Good luck.
