if you want to runn a 4g63 in your 420a body, all you need to do is get an evo 8 motor. the mounts are the same from what i understand. so its all ecu and wireing. i have no idea about the drive train cause i know the 420a is fwd and the evo is awd so that is something you would need to ask about.

also not that i have even herd of this but why not an SRT4 motor/internals. you could bore your block and run srt4 pistons and rods maybe?

this is just ideas off the top of my head anyone have insight as to this?