Old sub,
When I bought the bolt, it was a six lug 3600 with an open drive line possibly from a 56 or newer. The truck ran rough when I got it but I got it running smooth (relatively speaking).
I have made my decision to put in the LS1 with the t56. I think it a sound decision with fuel economy and power at the same time.
I still have straight axles up front and am deciding on whether or not to M II or the Camaro rolling chassis. Either way, I am going from a six to 5 lug for compatibility.
I know a lot of bolters would scoff at the idea of changing the drivetrain and suspension. Don't get me wrong, I love an absolute stock Chevy but for me and my daily driving, I need the reliability. I probably will not lower the stance of the truck either if I can help it.