Just for ***** and giggles, my son has a 99 Ranger XLT 4wd 3.0L v6 flex "V" in the 8th spot in the vin. It has a 5 speed, M5OD-R1 transmission. My question is to anyone.
IS THERE ANY AUTOMATIC 4X4 TRANSMISSION THAT HAS A FLOOR SHIFTER & OD ON/ OFF SWITCH THAT WILL MARRY UP TO IT?
I know it may need a different transfer case. It's something I've been thinking about this last week being confined in my home for the last week.

Or would a 4.0L with an automatic transmission fit in his truck?

 

Yes, there are a few
Any automatic can be used with a cable type floor shifter

A4LD, 4R44E, and 5R44E were all made with 3.0l bellhousing and 4x4 tail shaft, these all use same transfer case as manual

The 1991-1994 A4LD from a 3.0l Ranger 4x4 would be simplest, it doesn't strictly need computer control, you wouldn't get the torque converter lock up(TCC) as fast as with a computer, but you would have OD on/off available as a switch, on or off switch
Not much wiring is needed, reverse lights and OD on/off is all, you would use the same manual trans computer
You need to add a vacuum hose from intake to passenger side of trans
With the manual OD on/off switch you would in essence have a 6-speed, many off-roaders used this, 1st, 1st w/OD, 2nd, 2nd w/OD, 3rd, OD


For the 4R44E or 5R44E, it needs to be from a 3.0l engine and a 4x4 for correct tail shaft,
You do need computer control for shifting so you would need to change to 1999 3.0l 4R44E computer and transmission wiring harness, and add a button for OD on/off
OD on/off on these was a momentary contact switch so a button, it sends 12v to computer which toggles OD on or off, each time computer sees 12v is switches positions
A4LD is different, 12v is OD on, no 12v is OD off