first what are the heads, i looked up any GM small block head's who's casting numbers ended in 450 and all i come up with is 176450 used on 262 and 305 in 75'-76' and 367450 used on 262,267, and 305 in 75'-81' and to let you know that during this time neither of these motors even made 150hp, the 262 was actually rated at 110hp in 75-76' so that should tell you something about the heads that you are trying to work with.
you're gonna be no where near 500hp, maybe 350-360hp if you can get those heads to flow about 220cfm at your max lift
now before trying to pick a cam you need to know what pistons you are using and what the negative cc is in the piston crown so you can pin point compression with a .040" quench and what ever compression ratio you're gonna get. basically you need to know your compression ratio first then you can look for a cam, you also need to take into account what the motor is going into (weight), what gears will be used, what stall you plan on using, and what is the intended use of the vehicle. next i would question why you would use a hydraulic flat tappet cam with so much duration and lift, personally i wouldn't use a hyd f/t cam with anything over .480" lift and no more than 230 duration @ .050, past that i would look into a solid f/t cam, now if you have the money then you should look into running a hydraulic roller cam, with the 305H's cam specs on a roller cam that would be possible, but i think that the cam you have picked will have this 383 turing 6500+rpm (well past what the heads could handle) and the hyd f/t lifters will end up failing, not to mention the cam lobes. and then you mention a 600cfm carb
for a 383 turing 6500rpm (which this is what the cam you picked will want to have it running) you will need at least a 750 but i would certainly recomend a 825-850 carb. you seriously need to research what you want to do, and find some real combinations, cause what you have listed here is awfull