MACH I Member
Joined: Jul 2008
Location: Long way from home
Putting 3.8L crank/pistons and rods into a 4.2L motor turns the 4.2L motor into a 3.8L.
You can find forged parts, but they are not cheap. You'd be best off going to GSS Motorsports, SuperSixMotorsports or PM ESG42T. Those guys have more knowledge of what you're trying to do, most people that come here do not.
1988 Mustang LX coupe will miss you greatly
2004 Mazda 6s 5 door Sport w/5spd/3.0/RX8wheels/Kon/Eibach/and then some