Here I am!
Here we do get like 4 / 6 different brand for Slant Six headers, this is a very common upgrade. You can get those from low to high quality, and the price range for a new set can vary from ARP 300 to ARP 2000.- (USD 80 to USD 530).
The most common header here is the two piece 3-1 + 3-1 configuration, like the ones I'm running on my 1974 Polara RT. You got the collector below the steering box.
You can have them to fit power steering and air condition as well and they do NO block the starter, but sure it gets a little tricky to remove them.
But if you have a mini starter is an easy job, I have moved from regular to mini starter with my headers on very easy.
Here are some links to the best companies that produce headers:
http://www.caniossilen.com/ (the best company EVER in Argentina)
http://www.kiggr.com/Escapes_Especiales_Gobbo (used to be a Cañossilen partner)
There are also a lot of companies like ESCAPESSILENS (the one that Dan just mentioned) that produce the headers for the Slant, with good quality also, but not a top quality like Cañosslien, Gobbo or Maradona.
About engine bay fitting you have to consider that all our Valiants, Chrysler and Dodge cars share the SAME engine bay, bebeingt an EARLY "A" BODY design, from our Valiant V200 to our latest Dodge Coronado the engine bay is the same. Also for the "K" member and the steering box location.
SlantSixDan our Coronado / Polara / RT / GTX do not share the 67-76 Dart engine bay/wheelbase, they use the same engine bay and wheelbase as the Valiant IV (Dart '66).
If you are running a Slant Six on an 67-76 A Body I think that this headers are NOT the way to go, since this are designed to work on early A body engine bay with a very tight fit, you can make your own custom headers to work better and take some advantage of your extra room.
For the heat riser we rararelyare about it, if it's deleted better!!! When we think of moving to headers performance is the goal, so we do not want them (hotter mixture less performance.. you know how it goes).
So let me know if you have more question about them! I'll try to collect some pictures of cars with headers in different configurations for you to check.
Regards! Martin