The only reason I know about the one piece ones is I'm in the process of removing my oil pan on my 360 Magnum crate engine. I have to clearance it for the pitman arm and center link. It's in a 1966 Dodge Dart and has Doug's headers. I really don't want to pull the engine due to the headers. Not much room under the car. I plan on getting one of the one piece gaskets and hopefully, I'll be able to snake it in.
