I didn't comment because I think duals are pointless for most, and I didn't think that was the answer you wanted.
You said you didn't like two into one into two so I assumed that meant the Y-pipe idea.
Honestly though, what engine are you dealing with, and why do you want duals? If it's a v6 or mild v8, you said you can make your own stuff, weld up a 2.5" Y-pipe, merge the two 2.5's into a 3" single, and be done with it. If you want it for looks, then obviously you are going to have to do what you can to make some up. I'm not about giving up power...I've BTDT, and I know that running single is exponentially easier, with the Y-pipe being the most difficult to fabricate. But I made sure that the single 3" was enough to handle the output of the engine. Note that I've never seen a dyno comparison of an X/H-pipe exhaust vs. a properly sized single exhaust, nor even any commentary about expected results with the two compared.
If you are making some massive power, then obviously you need to size the pipe for that power. This chart is pretty handy when doing rudimentary calculations:
http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/#easy
Without getting into all the physics (unless you want to, David Vizard has a pretty good article on that), its best to run the smallest pipe you can that handles the engine output. Additionally, the less components you have to run, the easier routing is, the less it costs, the more you can spend on the components you do need, and the easier it will be to make sure it's hung properly, so you don't end up with things breaking or falling apart constantly.
Please understand none of that was said to insult you. Simply to provide information from someone who has spent a ton of time researching and making my own stuff, which maybe you hadn't considered or been aware of. It's your truck, and I understand some people just love the look of dual exhaust. If that is you, go for it.
