Exh manifolds in an Early A...

The 68/69 340 driver's will work, it's designed differently from the 70s 340 driver. You could sell the one you have and buy the other. You're in Texas, so am I, I have a couple of 70s 340 passenger's manifolds if you want to buy one for a real good price. You can also find a 96/97/98 Jeep Grand Cherokee 318/360 magnum passenger's manifold. Some FABO members have did a little grinding on the magnum passenger manifold to clear the inner fender on the '65 bodies. The Jeep manifold has an outlet hole (2 1/8" almost as big as the 340 driver.
The magnum and the 340 manifolds have magnum type exhaust port shape as opposed to the early (67-early70s 318)