Offshoreonly.com - Power Upgrade Question

I'd like to upgrade my engine package and I'm not sure which dirction to head in. I own a Checkmate Convincor 270 with a 496Mag(375hp). My goal is 500 reliable horsepower. I would like to be able to run periodically at WOT without worries (whenever my son comes with me boating, which is every time, he's not satisfied until we've done at least a few WOT runs........and I like to keep him happy!)
Whipple should be coming out shortly with a stage 3 package which includes a cam, intake, ECU upgrade, and exhaust mods. I think this is supposed to increase output by about 100 horsepower.
I was also thinking about an engine replacement by a reputable outfit like Kurt's Marine. This isn't something I could do myself (although I would love to), I have no tools, work area, or skills needed.
The Whipple idea would seem to be the cheapest, but I'm concerned about long term reliability. I don't want to do this again because I took the least expensive route. Also, what do I do with my current engine which has all of 31 hours on it? Are there outfits that will take it in a trade?
I don't want to go supercharger route with my stock motor.
I'm not sure which direction to head in.
I look forward to reading OSO posts daily and hope someone can head me in the right direction.
Thank You
AWelsh