hey dude welcome, sounds like u got plenty of money haha, wish i could say the same. the basic difference is that the LQ4 has lower compression than the LQ9 and has around 25 less horsepower. that would make it better if u plan on making it a FI engine. if goin N/A the LQ9 may be the better choice, the difference lies in the pistons and hardened rods. id go with a built 4l65e, as that is what the 6.0 is hooked up to in the SSS. idk any numbers on how much these r rated to handle or what the bottom end will hold either. ur gonna probably need new motor mounts too but thats a guess based on year differences. i wouldnt think the accesories would bolt up but idk redheartbeat would prob answer that 4 u.