360 magnum flexplate?

Im swapping a 318 magnum out for a 1998, 360 magnum in my 70 dart 727 transmission. I keep seeing that i need a weighted flex plate because the 360 is externally balanced but i can not find a single flexplate anywhere online thats for the newer magnum motors. all i can find is the LA360 ones. Can someone whose done this before please link me to the exact part i need to buy?