Algo mas , el 351M es un medium block , aca la explicacion :
When the 351 Cleveland was withdrawn after the end of the 1974 model year, Ford needed another engine in the 351 cubic inch (5.8 L) class, since production of the 351 Windsor was not sufficient and the 390 FE was being retired as well. To replace the 390, Ford took the 400 engine's tall-deck block and de-stroked it, with the shorter throw crankshaft from the 351 Windsor, and taller pistons, to produce a 351 cubic inch (5.8 L) engine whose components were largely compatible with the 400.
This engine was called the 351M and as a back-formation the taller-deck block became known as the M-block.
351M/400 351C
Nominal main bearing size
3.000 in (76.2 mm) 2.7149 in (69.0 mm)
Rod length
6.58 in (167.1 mm) 5.78 in (146.8 mm)
Deck height
10.297 in (261.5 mm) 9.206 in (233.8 mm)
The M designation stands for Modified, and is derived from the use of both "Cleveland" (block, heads) and "Windsor" (crankshaft) components in the same engine. A "Modification" for the parts intended application so to speak.
Many car enthusiasts of the day however did not particularly like this motor, due to the taller deck height and resulting extra weight. As such jokes about its use of shared parts (Cleveland and Windsor) began to circulate referring to it as a 351 Clendsor.
Later car enthusiasts
incorrectly refer to this motor as a "351 Midland" presumably a reference to Midland, Michigan a city just northwest of Saginaw.
