can i use a one piece magnum sump gasket with a LA pan?

Hey guys
A while ago i built a 360 magnum and kept the magnum timing cover. All i changed was the sump from a truck one to a LA pan.
It didn't seal very well but i have heard guys using them. Im not sure if it was because i used the magnum timing case with the LA pan or if my pan was just old and damaged.
Anyone used the one piece gasket with a LA pan and the magnum timing case with no oil leaking problems?
thanks