Originally Posted by S10 Racer
They will not bolt up upside down.
Good catch i think you are right the bolts on bb are not in line like sbc. They are offset bolt pattern in the picture. Once you turn them upside down they will not fit. You could use a few tricks to make them fit if this was a rare engine and parts were hard to find. But for chevy i would not waste the effort to make them work since other options are pretty cheap.
Do you have a wire feed welder. You can buy kits with manifold flanges and header primary pipes included if you need them but i would think a log manifold would be ok in this case. It would need to be pretty big but not to hard to make your own. I have had to do it on several cars. It seems to be easier than trying to weld to the old cast iron it will resist all efforts to weld up correctly and stay that way for any length of time.
You can also buy manifolds and pipe kits setup for bbc and sbc. Bbc might be costly because a bbc with twin turbos is almost always a big build up in the 1500 hp range. Mild turbo builds for big chevy have a smaller market. But imsure so,eone has a nice kit out there if you want to buy one and be done.