FWIW, I just completed a rebuild on my 67' 400 engine. I estimate that the rebuild, including parts, labor, etc. cost me $6,500. This was with considerable sweat equity and working every angle to keep the costs down. Rebuilding these cars is a labor of love and you'll rarely get your money back if you want to sell the car in the future. I am not sure that I would do it again as buying a crate or rebuilt motor would have cost just a bit more but would have saved me time, effort and stress. This said, you cannot find many 400 or 428 cast iron engine blocks that are worth rebuilding and no aftermarket blocks for Pontiacs like what you can get for a Chevy. While you can lighten the overall drivetrain weight with aluminum heads, the cast iron heads perform well if you can restore them. And aluminum heads are expensive. The old saying that "there is no replacement for displacement" may lead you to want to rebuild the 428 but there are certainly good options for rebuilding a 400 as well.
