I just got a Mopar Performance M-1 2 barrel intake. It does look a lot better than the factory aluminum 2 barrel intake. I puzzeled about one thing, what are the two 1/2" pipe thread holes for in the bottoms of runners 1 and 6? It came with one 3/8" pipe plug for the vacuum line port (the tefflon tape on it was wrapped backwards) but no 1/2" plugs for the holes on the bottom.

Cecil

My guess is that these two tapped holes on the bottom of the runners were made by the foundry, as an easy way to support the casting's sand core.
I would bet that these bottom holes are about 1/2 way up the end runners.
The rough casted holes left behind from the casting process were later drilled and tapped for pipe plugs. (thats cheaper and more reliable then welding them-up)
DD