Here are some photos of the "Dutra Duals" cast iron exhaust manifolds for the Chrysler Slant Six. The front manifold is a new iron casting collecting the front 3 cylinders and has thick walls plus good flow. The rear section is a modified factory casting.
A closer look at the modified factory manifold I use for the rear section. This keeps the factory carb. heat riser valve and the stock automatic choke mounting pockit. You can also re-use your current exhaust pipe but it is better to have two new header pipes made and fitted to the new manifold set. The outlet size of both the manifolds is 2 inch. Here is a good view of the capped-off section (welded on).
See http://www.slantsix.org/articles/exhaust-man-mods/exhaust-manifold-mods.htm for detailed "how-to" info. on making your own rear manifold section. The major issue I have in making these units up is finding a good factory exhaust manifold to use as a "core".
This group of photos shows the routing for the new front manifold's exhaust header pipe. The stock pipe below is hidden. The "Dutra Duals" can be used with any intake but there are special needs for each intake which needs to be addressed.
It is interesting to know that this dual manifold set-up idea started as a result of "hand fabbed" units. After doing a few sets this way, ( the "hard way") I went ahead and made-up the casting equipment to do the front section.
The latest version of the Dutra casting now has a larger outlet flange and larger mounting tabs. This allows the unit to be machined for use on the front or rear 3 cylinders. The large outlet flange is designed to accept the mounting of a turbocharger but truth is that doing this takes a lot of custom work, seeing that the starter motor is in the way. "Dual Dutra Duals" can also be done but click here to see some of the issues involved.
Be sure to check-out the Slant Six Message Board and tech. article section at www.slantsix.org
Doug Dutra (Doctor Dodge)