425 pistons are not fungible
with 455 pistons due to a different distance from pin center to top of piston
("compression height"). The compression height for the 425 is
1.595" and the 455 is 1.720". Compression height is the distance
from the center of the piston pin bore to the top of the piston.
Compression height refers to the placement of the wrist pin. With any stroke
and rod length combination, the pin has be in the right place to complete
the picture for a block of any given height. If the stroke is increased
the engineer has to either shorten the rod, move the wrist pin location
closer to the piston crown by ½ of the increase, or make the block taller.
If there is room they usually leave the rod alone and change the piston.
This is probably cheaper and makes a better rod angle which cuts down on
piston and cylinder wall wear. Sometimes there isn't room below the rings
and other places, so it's easier to shorten the rod. Either of the other
two options are cheaper than making the block taller because this changes
lots of other things, such as intake width, pushrod length, location of the
The 1965-67 400 block will take a 350
piston with a .057" overbore. The 350 pistons are readily available in
a variety of compression ratios.
The diesel rod is slightly shorter than the gasoline rod,
for the increased ring-land necessary for a diesel, I'm assuming.
[ Thanks to Chris Witt, Walter, Steve, Bob Barry for this information ]