Better Stock Manifolds for '83 K20 4x4?

[MARKDTN]

I have an '83 K20 that my uncle bought new. I drove it to 150k miles and then a cam lobe went down. I put a complete '91 L98 Tuned Port engine from a Corvette in. Motor is completely stock. I went from 14 mpg to 17, but now I have to run premium fuel. Anyway, I put back the stock exhaust manifolds. I have 2" true dual exhaust with Walker high flow cats and no mufflers. I think the stock log manifolds are restricting my flow. I have a set of Vortec manifolds from a '98 truck. I also have the manifolds from the '91 Corvette and a set of '94 LT1 Corvette manifolds. I have done a few searches, but can't find a good answer. What is the hot tip on cast iron manifolds that will fit a 4x4 3/4 ton in a 73-87? Preferrably ones that I can buy a stock headpipe for, but that is not a deal killer. I do not want headers. Thanks!