internal or external balance

Are you sure about 68 and up being externally balanced????I was always thought they are internally balanced (don't know about the magnums)...I have 3 here and most parts interchange with the 340's. The only externally balanced motors I know of are the 360's and the 73/74 340's...but I've been wrong before???
checked the book by Larry Shepard on the small block...page 18 has the info...the 318's are internally balanced, they have a cast crank thats lighter then the 340's and the pistons and rods are lighter. If you bolt a 318 into a 340 you must rebalance it!