This guy has done a project page on this type of aod. I think this one is the electronic style, but the earlier style can be used with a little less trouble. Big project, good luck. I have a 66/289 3speed and would like to do this one of these days...
5.0 and the late 80s 351W car AODs are a direct bolt in for the 6 bolt bellhousing 289s. You will need a 28 oz balanced flex plate since the 5.0s have 50 oz. All Ws are 28 oz balance flexplates and bolt right on.
I think the C-4 flexplate bolts right in. Check it. Flexplates are readily available for this swap. Speedometer cable should hook right in. All you have to do is move the trans member a couple inches rearward and shorten the driveshaft one inch, and the newer starter. I think. :thumbup:
You will love the AOD if you have about a 3.50 gear or lower. The low torque engine does get a little soggy in AOD if you have 3.00 or 2.80. Your overall gear ratio gets to be 2.00 or less in AOD (.67 OD ratio x rear gear ratio).
Install the trans and drive it to see if you need a change of rear gear.