I agree with john, and not only cause the front of our trucks are damn near identical. You're leaving a lot of things out of the equation. You're swap would be closer to 8k by the time it's all said in done. Now if money is no object, drop the bad mofo 572 in there and have a hell of a toy. I too like big block ole skool power. If money were no object the 572 would be my choice for the c10.Sick idea though! If u have the money to play with I say do it!
2003 SIERRA- 5.3 DD
1985 SWB C10- slow, future plans- shaved, painted, 6.0/4l80e