You can call them to discuss technical questions (such as hook up to your hookers) but for purchase, price will be the same as a local dealer. As mentioned, that's their policy.

As you have a stock motor, but with headers, I think we (those who have responded) assume you are interested in maximizing the power while keeping it fairly quiet.

If so, then it seems logical to basically go with a stock style arrangement; but with modifications to take advantage of the headers. While the best source is factory lit (such as shop manual), poking around the web it looks like a 440 e-body came with 2.5" head pipes, mufflers, and resonators and some sort of rectangular tip.

http://www.gardnerexhaust.com/1970-mopare-body-exhaust-system.html

http://www.cuda-challenger.com/cc/index.php?topic=102566.msg1013749#msg1013749

http://www.cuda-challenger.com/cc/index.php?topic=102566.msg1013749#msg1013749

While the Hemi cars were similar they also got an H pipe.
I'd suggest keeping the collector diameter at 3" until it intersects the crossover in the H. Then drop to 2.5" to the first muffler/resonator.

Also, as the most restrictive point in almost any system are the mufflers, this place to look for improving flow at higher rpms. Higher flow can be achieved by larger diamemeter in/out. So if you go with a single muffler each side in standard location like you have now, then definately go with 2.5" in/out. If they are all the way in the back by the tailpipe, the restriction on flow will be minimized because of cooling and some energy will have been reduced in the resonator.

You'll have to do some measuring to see if there is room for an X. I think in this particular situation, an H will serve better (for sound reduction and placement). If placed on the harmonic, which is probably around 20" from the primaries, there is also a possible increase in torque and power.