G/ED doesn't allow fuel injection (even though the 4.2 came with it. We are using 3, 2 barrel carbs. Currently we are running a Powerglide 2 speed, but we definitely could use another gear. We plan to eventually switch to a 3 speed. We did have to have a custom aftermarket SFI approved Flexplate made for this engine, as there isn't an off the shelf one available. I'm notsure about the 5 speed flywheel as we use automatic transmissions. Inline motors do present different balancing issues than a wedge style motor. The process of balancing the cranks is different as well.
I hope I touched on everything for you.