Factory short block 5.9, EQ Heads, AirGap, camswap and good carb (and headers) make for an easy low to mid 12 second Abody. There are a few of us that have done it.
I love my junkyard 5.9 magnum. It is turbo'd now and I've been running it at around 6psi for a couple of years which I believe puts it close to 475HP. I recently turned up the boost to 10-11psi and it's absolutely violent in this little Abody. Probably closer to 550hp at that pressure. Not sure how long it will last but I keep it under 5500rpms and watch my tune carefully.
