Ford 335 engine - Wikipedia, the free encyclopedia
the 400 and 351M are in the same engine family but have a taller deck height than 302C & 351C, 10.297" vs 9.206"
wider intake, larger diameter main bearings, longer connecting rods, larger dia wrist pins, longer pushrods & oil pump driveshaft. engine mounts are also different
same cam, timing set, rod bearings, front cover, valve covers, fuel pump, oil pan & pump
they also share the same head gaskets & bolt pattern so any 351C head will bolt on but there were never any production US style large port 4V intakes produced for the 351M/400 so 351C intakes with spacers are used for 4V or aftermarket alloy head builds. CHI does list a 400 intake for their heads