DXTAC, I would find with somebody that has swapped in a 4BT and ride in/drive it before you get serious about. Those 4BT's are loud, vibrating little engines. They don't make great power in stock form, and need the pump turned up and injectors to make really good power. Some people love them, but I'm not fan. A friend of mine put one in a Jeep and regretted it ever since. I love the 6BT's, but wouldn't swap a 6.2 for a 4BT. I'd build the 6.2, add a turbo and you'll get comparable power and will be much more pleasant to drive. You could do it cheaper and much easier as well. JMO.