are you talking about the stainless steel tube manifold they put on the passenger side only of some early astros?
Both of my 87 Stros had the SS Tubes on passenger side, cast iron on the drivers side...
I believe there was a drivers side manifold of that type in some of the 4.3 4bbl equipped trucks from early to mid 80s. (see pix)
I thought they might be a good cheap improvement, so, I looked at a few, but decided not to bother as they didnt seem like they would be much of an improvement over the cast iron ones.
The tubes are crimped in to make the bend right where they meet the head. Looked restrictive, a lot. Certainly not mandrel bent tubes.
If you need one for the drivers side for some reason, try looking at around 85 1/2 ton trucks with a 4bbl 4.3. PIX = 1000 WORDS