I prefer daul pattern cams, the Magnum is a single pattern, and what that means is, the single pattern has the same duration and lift on both the intake and exhaust. With a daul pattern, the exhaust is usaually held open longer and lifted higher to aid in evacuating the spent gasses. They will generaly make torque over a wider RPM range. Two suggestions I have are, Crane PowerMax hydraulic flat tappet part#270-113942, 272/284 .454-.480 lift, 1800-5600 power range. The other is Comp Xtreme Energy part#249-12-242-2, 268/280, .477-.480 lift, 1600-5800 rpm range. Both cams will work with a stock converter, have good street manners, be under the max. lift that a Vortec head can use and make torque over a broad, flat curve. Either will funtion well with a pump gas friendly 9.1:1 comp. ratio. Valve lift should be as high is as needed to allow the mixture to pass for sufficient cylinder filling. After a point, a given valve diameter will not flow any more, no matter how high it's lifted. Duration is how long the valve is open, referenced in crankshaft degrees. Duration at .050 is the industry standard, when appreciable flow can pass the valve and seat. It can also tell you how fast the cam is in regards to ramp speed by subtracting Adv. duration from Dur. @.050. The lower the #, the faster the ramp speed. Use this calculation to compare cams. There is a limit to how fast a flat tappet cam can be due to lobe-lifter interference, this is where a roller cam really shines. Since the roller is running on the lobe with a wheel it can follow a much more aggressive ramp ,be held at the nose longer and stay within the same duration specs as a much smaller and slower flat tappet. Cams with dur.@.050 over 230deg. start needing a higher static comp ratio to overcome cylinder pressure losses due to a late intake valve closing point. Lets say a cam is closing the intake valve at 90deg. ABDC. The rising piston that is now in the compression stroke, and the intake valve, still open for 90deg., almost half of the compression has been pushed back out the intake valve. Therefore a higher comp. ratio is needed for that cam to function in that engine to make up for the loss. A late intake closing point can be usefull in a high RPM engine where the intake charge is moving so fast that it ia advantageous to leave the valve open to take advantage of the ram effect. Lobe seperation angle is refferenced in camshaft deg. It is the angle the intake and exhaust lobes, at the nose are distanced from each other. Wider LSA's, 110-114 are suitable for a street engine. I did not see what the Crane had, it's probably 112. Check out the two cams I mentioned, call the manufacturers and give them your full details. Any other particulars you have, I will try to answer.  JW.  

Here is another combo that I used on a costomers 383 stroker with great results lunati cam&lifters p#07102LK which has a .507lift 2200-6200rpm range, aweiand X-celerator intake p#7546, a 650cfm double pumper holley carb., a set of summit heads p#sum-152123, 10:1 C.R. and aset of 1.5 ratio roller rockers. Also I use a eagle rotating assembly.  

We have built quite a few 383's over the years and in this build in this link http://www.chevelles.com/forums/showthread.php?t=106715 we used AFR's and the builds with a good set of NON MEXICAN casting is a good place to start as the Mexican casting seem to have smaller intake runners then the older 906 and 062 castings. And with the good Vortec castings the dyno were identicle to the one in the link.

With the Vortec heads and the fast burn chambers on the dyno we have only needed 28 to 30 degrees of timing on these engines and they will be less prone to detonation.

The block you have picked have it sonic tested to make sure the cylinders have the proper thickness and don't go by  core shift as we have found that not to be very accurate.

If your looking to build some big HP and torque you may think about adding billet 4 bolt replacement center caps or go to splayed as its not so much the HP or torque that will try to move the caps but the added stroke. We have seen quite a few times the problems with not using good caps for the intended HP for the engine being built.

If you are going to go with a forged rotator the Callies Compstar cranks are a good choice as the journals are dead nuts right on from journal to journal and they are straight compared to the Eagle and Scats.

We can buy 4340 cranks for 370.00 but their not quality peices as far as sizing and straightness at our shop we go with quality before pricing.

We do a lot of crank balancing for other shops in the area and we have seen alot of promblems with journal sizing and straightness.

Rods we have been using the Callies Compstar or the Scat Procomp 6 inch I beams and the Mahle pistons are a good choice. So far all the 6 inch rod cranks will internally balance that we have done.

A callies kit would run about 2050.00 with crank, rods, pistons and rings, rod and main bearings and balanced.

Same kit with Scat Procomp rods is 1950.00

Here is another link to a engine we had on the dyno a few weeks ago http://www.chevelles.com/forums/showthread.php?t=236517 and this engine and the one in the other post had single pattern cams.

One other area that is over looked is the duration at .200 which we consider a HP numbe in a cam.

It all boils down to what you have to spend and what you can get qway with.

Good luck with your build Carl