I have a 260 V8 with a manual transmission. I want to put in an automatic. Is the driveshaft the same for both? Are there any other issues?

 

Driveshafts should be the same. At the most you would have to swap the yoke.
You are looking at a major issue/challenge. The 260 requires a unique 5 bolt bellhousing. The first 289s were like this also. Many of these cars used the 2 speed slushbox which you must avoid.
All other automatic bellhousings are 6 bolt and can be swapped from one engine to another all day.

I have a friend with a Falcon graveyard and he should have a bellhousing, but I don't know if a later C4 will bolt to the early bellhousing. Not that an early C4 is bad, just harder to find.

 

I have a manual 64 1/2 rebuilt tranny in excellent cond. ready for shipment in my garage if you just need a new tranny.
Have pics if interested.

 

I already have the 5 bolt bellhousing. I wonder if it will match a laterversion C-4?