Yes, conflicting info, and that list only adds to the misinformation.
Here are three ebay and one Autotrader '84 and '85 5.0L Mustangs with an "M" engine code and EFI/AOD:
'84 GT convertible w/ "M" EFI 5.0L and AOD
'84 G.T.350 hatch w/ "M" EFI 5.0L and AOD
'85 GT convertible w/ "M" EFI 5.0L and AOD
'85 GT convertible w/ "M" EFI 5.0L and AOD
Also, the 5.0L engine code in '87 was not "M", it was "E", just like every other non-SVT Cobra '88-'93 Mustang. From the Door Tag gallery on this 'site:
1987 Texas Department of Public Safety Door Data Sticker. DSO 57-0119. Matt Buckmaster photo
Notice the "E" engine code.