LS3/LSA Bottom Mount T4 Turbo Exhaust Manifolds
These schedule 40 SS manifolds come with a lifetime warranty and will give you exactly what you are looking for, for your turbo build! They are Single scroll T4 with Single 44mm Wastegate Flanges.
They were designed around EFR 9180 1.45 AR turbos (Biggest we could find! :)) They will hold any smaller Turbos with T4 housings including:
GT40r
GT35r
GT30r
Precision 6262
These manifolds fit the 2009+ CTS-V with either the stock LSA block or upgraded LS3 and LSX Block configurations. They are also suspected to fit 2009+ ZL1 camaro and other LS applications. 
Please allow 3-4 weeks for build time.
LSA Turbo Manifold
LS3 Turbo Manifold