Just to clear any confusion, the 400 is referred to as a 400,
the 351 version of this engine is referred to as the 351m,
because it is a modified version of the 400.
Yes, it's wider, taller and heavier than a 351, and the
stock heads basically suck because of the open non-
quench comb chamber.
However, Cleveland heads will fit right on, including the
now available 2bbl closed chambered ones from AU, and
the new aluminum closed chamber heads I just read about.
I've read build ups for things like Pantera's where there is
sufficient room that got well over 400 hp and torque using
good Cleveland heads, Cleveland 4bbl intakes using either
the Weiand or the
www.pricemotorsport.com adapters, and
a good Cleveland cam.
Having said that, they are more suited to trucks because of
the size of the engine, although they're still quite a bit
smaller/lighter than either FE's or 385 series. With all the
good heads now available for the Windsors, the 351 W's
are much better overall for most car applications simply
because of the size and weight issues.