I lost track of the Vortec needs. The TBI Vortec is still not the best choice. It is a copy of a factory manifold. If you are not forced to use EGR there are plenty of good carby intakes available that would work with adapters.

Coolant under the manifold is to aid emissions. It is not there for cooling. The bypass in the old block exists to circulate coolant from below the thermostat ensuring warm coolant reaches the 'stat and causes it to open. You can do the same thing by adding a small hole to the 'stat (about 1/8"). If you aren't in an area where it gets really cold this won't cause problems. If it gets below 20 deg the engine might not warm enough. Additionally, you can install small nipples and use 3/8" hose to create a small bypass path to the water pump. What you do not want to do imo is use 1/2" heater hose to create a bypass path. The stock intake has a dual valve 'stat that closes the bypass as it opens the radiator. A traditional 'stat cannot close the bypass path and a 1/2" hose may allow large amounts of coolant to bypass the radiator.