Oh, come on, you shameless barter you. You'll be ok as long as you don't have the tools and skilles needed to make the parts as well as they have to be made.
FWIW, I spent several ages designing the bracketry for my tandem rig. Simplified, reduced the amount of machining needed, ... There's no way I can drill plumb holes exactly where I intend. And there's no way I can turn the key part of coupler from any material. Don't have the tools, am out of practice, and wasn't a very capable machinist when I had access to a reasonably equipped shop and used it.
So after I had the designs more or less done, I talked things over with Adam at SKGrimes and HE's drilling holes and turning the tube for me. Some jobs are better farmed out. You do what you're good at, let the good machinists do what they're good at. By the way, Adam made some suggestions about choice of materials and fine details. Of course I accepted them. Same thing happened the last time I had an, um, odd job for him.