Unless you can buy this for $1500.00 or less, I wouldn't place a bid. Figure on rebuilding both engines, electrical systems a mystery, if it's had water might have to replace both MPEM's. You could spend 4,000.00 before you even get it to the water, and that's doing all the work yourself.
At $1500.00, at worst you could part it out, sell the trailer. Also if water is in the engines they may not even be rebuildable cores. I don't know when they stopped manufacturing 2 engine challenger's you can google it. Parts shouldn't be a problem but at what price?
You should probably post this in the 2-stroke boat section, those guys would know more.
Lou