My "new project" have the 496's. I could sell the Avanti with no power, then I would still have to sell the 496's.

Staggered 38' white and blue race boat with the #3's that was on ebay? That Would Be Sweet With Some whippled 525's

Right, however in your case it makes more sense to sell separate than together. The mismatch of years between the boat and motors are going to be a huge drawback in your sale. If it was an older boat and newer motors it wouldn't matter. Also, as you stated your going to have to pay someone to install the 496's, so not only are you throwing good money after bad (old motors in newer boat) but you may be adding cost to the buyer if he decides he wants to rip out. In my opinion, you list boat without motors with the option of having them sold with/installed and list the motors separately.

While it is a cool boat.....lots of options out there from competing 37-42 ft boats........I wouldn't swap out for old motors, just makes the boat more oddball.

If you want a real world opinion, call Shogren at Pier 57 and run your idea by him. He is probably one of the few people that can put real world numbers on the deal.