Working on cam specs for a 10:1 compression (checked this so it really is 10:1) 383 with 516 heads with the 2.08/1.60" valves. Car has a Performer RPM intake and headers. I know the LCA and overlap I want. All I want to know is single pattern or dual and if dual what the duration difference between intake and exhaust should be. Thanks!

What kind of car is it going in? What gears? Trans? Purpose?

With older heads I do like split duration cams...you'll usually see a 8-10 degree duration split in most off-the-shelf cams.

The duration split should be almost wholly dependent upon the intake to exhaust flow ratio after the compression ratio, intake and exhaust systems are accounted for. I know all the other parameters for my cam which is why I asked this one question. I need expertise from someone who has worked with these heads.

Given that you seem to know what you want, look up the data you want here...or better yet, get your heads flow tested and figure it out.

Headers or manifolds? Free flowing headers favor less or no split. Manifolds probably like the split.

Call the experts, Hughes, Comp Cams, etc.