TTI BB headers...in an A-body?? Tell me your story...

Can You install the tti headers on the engine and then install the engine from below? Or do.I ha e to fit them while installing the engine? Or do you have to drop the engine in from above? I want to build the suspension/brakes/engine combo and install from below. I have 2" headers if that matters.
The factory was to install the engine from underneath. On my 73 dart I layed the TTI 2 inch headers in the engine bay frist and had two friends hold them while I dropped the engine/ trans in. I thought it was going to be a pain in the *** but I had the engine in less than a hour