I think what you are currently doing with the trailing arms is perfect. I love the idea of cutting them, and then making them stronger where the u-bolts go through, rather than how they were from the factory. One thing you should make sure that you do with the trailing arms before you even bolt them up to the axle, is beef them up one way or another, because we all know that once you get a d80 you are going to want to beat this rig a little bit more than you did before. (whether on purpose or not, it will happen) The way I would go about making them stronger is welding the 2 pieces of c channel steel together about ever 4-6 inches with a 4-6 inch seem. Then build a piece of steel to go on the outside of both of the c channel pieces, and if you can, I would dimple die them.
Typically what I have done when it comes to welding on the perch that the u-bolts come through (or spring perches for a leaf spring truck), is get it eyeballed where you think the pinion angle should be, put a couple good tacks to hold the 2 together, then take an angle gauge and check it to fine toon it exactly how you want the pinion angle to be.
One problem you are going to run into is shock mounts. The factory c10 mounts are not going to even come close to working. The factory dodge mounts will not work either unless you want to modify the mounts on the frame. The way I would go about making them work is just buying some universal shock mounts that you can buy from almost any suspension specialist, and putting them in a spot so that you can use the factory frame mounts.
Here is a website for an idea of what you can use for shock mounts
http://www.polyperformance.com/Syner...g94RoCFMDw_wcB