Yes to using the rag joint as a turning aid!
Just no need to fully install and tighten it down to find your steering center point. Depending on how the rag joint ends up alignment wise, after you mark your points, then you can pull it back off and reposition it the way you want it to look. I'm with you on not wanting to do too much on your back on the floor pushing that gear box up and in place - Blah! You could use an undersized diameter long bolt slid part way into the upper gear to frame bolt hole. When you get it up high enough, push the temp bolt through and into the frame to take most of the weight of the gear off your arm while you work on getting more correct sized bolts in and started. Be safe and post some pictures as you can please.
