If the truck you are looking at with the 5.3 is a 2WD automatic, maybe consider using that transmission also. OD would be nice with the 3.73 gears. You also might be able to do some simple mods to the /6 k member to make it work. Look around in Alex5280's build thread about how to do it. I'm pretty sure it was him that converted a /6 k frame to a small block spec with minimal hassle. I'm in the middle of putting a 5.7 Hemi in a 70 Duster with a 74 V8 spool mount k frame. I'm using a car motor, and TTI told me right up front that the headers wouldn't fit that setup and still have the AC compressor in the stock location. I re-engineered the drivers side mount, and it fits now! Point being....with a little patience and head scratching, you can make about anything work. Have fun with your swap, and good luck. :)