A 400 (406 cid) with 180cc Dart Iron Eagles is the way to go for torque.
If you are required to run exhaust manifolds and require a stockish idle then get a cam with 212-214 degrees on the intake and 10 more degrees on the exhaust with 110 LSA.
Use D-shaped piston dished to drop the compression to 9 to 9.25:1. Use a Q-jet with a stock gm high rise cast iron intake. Don't use a JET q-jet, they suck. You will need to spend about 500.00 to get a good Q-jet.
As for timing, 15 degree initial and 37 total should do it.
You will not be able to find a 4bbl cast iron intake that fits the vortec heads.
it would be better to use cast hyper pistons (quieter).
It would be nice to use 5.7 inch rods but it will cost more money and knowledge to set that up right.