You are trying to get in the house thru the basement door ......use the front door. First off forget vaccume readings....a vac boost can is like 50 bucks and you can use any cam you want,Second forget idle quality ,you threw that out the window when you went for 500 hp.
Match all the components together for your goal and let the idle and vaccume find where they want to be...not where you would like them to be.The idle and vaccume your motor will see is already set by the cam you chose.
Set a goal and let the goal tell you what parts to buy for the engine.Then match those parts together and let the motor be all it can be.Do not pick a 500 hp winner and then cripple it with trying to get the vaccume up or idle down.
Sounds like you want a race car in a truck that runs like a stocker.Your goals either need to be idle and vac quality or peak hp.Trying to get tooo many things from one engine will only insure it does none of them well...

The only way to get what you are telling us you want is fuel injected and supercharged.Idles well ,gets good gas mileage,and has a good vac signal and makes power.A 500 hp carb deal in 383 ci is not going to be friendly to daily driving ....unless 1000 rpm idle and low vaccume and trans coolers everywhere are acceptable and you had better keep lots of tuning tools with ya if the weather changes too much on you while your out!!!
Now if you were doing 500 hp with 550 cubic inches then this would be a different story.