There's a lot of 4.2 swap discussion on V6Power.net;
Several Stang owners have used the 4.2 shortblock
with single-port heads, or swapped the 4.2 crank /rods
/pistons into 3.8 blocks.
The 4.2s and late 3.8s use longer rods, and short pin-height pistons, but are made of soft "powdered" metal,
and the crank is nodular cast iron.
SC or 351w rods would work, with custom forged pistons,
but it's still a cast iron crank.
Some Stang guys are running centrifugal chargers on the 4.2s,
but the Eaton charger is supposed be much harder on the bottom-end, because it makes so much boost so quickly,
and more load on the crank nose, to drive the blower,
so no-one, to my knowledge,
has put a 4.2 shortblock under an SC top end.
It's not that turning .010 off the rear journal is any problem;
it's whether the cast crank would survive.