I have a 383 4 speed. Bought Schumacher headers new and at the time they sent them out to modify the left one for the stock Z bar.
I have aluminum heads, and spark plugs are incredibly easy to get in and out. Socket, rachet, and one short extension for a few.
Headers do not interfere with Z bar or anything else. Recently went with new gaskets, forget the brand but reusable, no problems changing them.
If needed, can remove headers by unbolting engine mount and raising a bit.
Getting every bit of power wasn't my goal, so I didn't look into that part.
