I do appreciate all the responses. I don't have a particularly large lathe, so turning a square or rectangular piece isn't easy. Maybe with a larger lathe it would be easier, but I don't have a need for a larger lathe where I'm at.
Sounds like using a rough guide to cut the piece on the bandsaw is the most sensible approach, and maybe as I get more acquainted with turning I can back that down and let the lathe do the work.
"Sometimes I lie awake at night and wonder - what have I done wrong. And then a voice says to me, 'This is going to take more than one night.'"