If you get the factory engine harness with your donor, you can have it sent out to be reworked. I had speartech do mine, nice quality work from what I can see on mine. A local guy did a 5.3 motor in that body style nova with a cowl hood, and all the truck accessories/intake fit under the hood- barely. I am not sure what motor mount setup was used or if he made them himself to gain some clearance. A 6.0 would be the same fit
A nice cam, long tube headers, and a good tune should get you close to 500 crank HP. Keep us updated on your project!
Scott