Take the flexplate off. Line it up on the converter so the offset bolt line up properly, mark both converter and flexplate. Line up marks once engine is installed.
318 and 360 have the same bellhousing pattern. If the converter is a 318 piece, it needs a weight or you need a 360 balance flexplate.
I have the flexplate that came with the 5.9 magnum, plus an extra. Sounds like I need to unbolt and move the trans back to access the converter and flexplate after the 360 magnum is in.