The present day Melville ferry is approximately two and a quarter to two and a half miles south of the location of Morgan's Ferry.
E-mail me your address, and I'll put a copy of that part of the map in the mail to you, along with a copy of a relatively recent topo map. If you have a topo map (you should be able to find something on the Internet), the west side of Morgan's Ferry was in Section 8, north side of Melville. It's a little triangle-shaped section. The topo map edge passes right through the area we're interested in (funny how that always happens), but it looks like the West Morganza Spillway Guide Levee hits the Atchafalaya about where the east landing of Morgan's Ferry would have been.