There has been some discussion about what flywheels and starters the 351M and 400 engines take.  And, from the attached 1980 - 89 Ford Master Parts Catalog entries I can see why.  But, Bubba's site clears that up very nicely.  It says "Both 351M and 400 engines have the same 28 oz-in crankshaft imbalance, so all M-block flywheels have the same balancing counterweight, and they can be interchanged without vibration or balance problems."  But, Ford muddied the water in 1985 when they issued a replacement manual transmission flywheel (E5TZ-6375-H) that is drilled for both 11" and 12" clutches - as shown on the 1989 era MPC captures below.

So:

• Automatic transmissions: Both engines take D1AZ 6375-A flexplate, which is the same unit used in cars from 1971 forward
• Manual transmissions:
  • 351M: D7TE-6375-A  This is drilled for an 11" clutch, and probably used in trucks from 1977 forward given the "D7".  Tim Meyer says "11" flywheels have 3/8" evenly spaced bolts."
  • 400: D7TE-6375-B, which is drilled for a 12" clutch, and probably used in trucks from 1977 forward given the "D7".  Tim says "12" flywheels have 5/16" bolts in 3 pairs."

But, that leaves the question of what starter.  Well, Bubba says the ring gears were all the same on the flywheels (D7TZ-6384-A).  However, from the parts catalog it appears that Ford replaced the earlier starter (D8AF-11001-AA) in January of '81 with a revised one (E1TF-11001-BA).  I don't know what the differences are, but since the flex plate and ring gears didn't change then the starters are  interchangeable.  And, note that the catalog entries don't differentiate between automatic and manual transmissions - the same starter works for both.