Keep it simple, cast iron does not weld easy, not for a shade tree mechanic.
If you have $$$, & you want the simplest turbo install, then get the SPA exhaust manifold.
If you do not, just use a 292 2.5" 3 bolt exhaust manifold.

Examples:

http://www.ebay.com/itm/SPA-Turbo-T3-T4-...778afa9&vxp=mtr

http://www.ebay.com/itm/Chevrolet-GMC-23...b8ae76d&vxp=mtr

http://www.ebay.com/itm/NEW-CHEVY-292-EX...=item4ac9553452

MBHD

12 port SDS EFI