techically, they are pretty simple, a little bit of geometry to get the balljoints clocked right and the best shock mount location, after that they are easy to jig. Practically, a lot more difficult. everything neds to fit tight before welding and you need to be a damn good tig welder. A swingarm, you can fill little gaps welding, mig weld it, screw up a weld, grind it out and reweld etc... you just don't have that amount of foregiveness with a-arms. I have been in Laegers shop when he is making custom a-arms, the guy is amazing, has the bend radiuses in his head, fits stuff together without thinking about it and can lay incredible tig welds with his eyes closed.