300 HP is easily doable from a 283. With the proper heads, exhaust, intake and carb.
What I also want from this is a good "lumpy" sounding cam.
No No No and Hell No. Lumpy cams equals High RPM drag strip cams. What I am telling you is the more duration, higher lift cams do not make any power until 5000 and up RPM. Are you going to run this motor on the street at 5000k RPM?
Take of a plug wire or vacuum line and you will get lump. I am not a fan of Comp Cams, very hard on the valve train, and noisy as well.
Here is my suggestion
Have your 283 built with good internals, crank, rods, and pistons Find a set of Power Pack heads and have a mild port and polish done on them. Look for an Isky 270 mega cam for that motor. The LSA in that cam will give enough lump. Good headers ( I like hooker), dual exhaust. Edlebrock Air Gap manifold, and a 500-600 Holley 4160.
Next 700R4 is a good tranny but you will need a 2200-2800 stall or one from a late model Corvette. Have the tranny set up so when you are cruising it does not shift into higher gears so you "lug the motor",
several shops can do this for you.
Next is your rear gears. With this setup I would go with a 3:73 Eaton posi. Very stout, and good gears, with the 700R4 a very good combo street and highway.
You will be using premium pump gas, make sure your engine builder gets you into the 9.8 area for compression..
Also it is a myth for the 400 Chevy motor overheating. Have several friend who run these in AZ
