Guys, can it...Ii've seen overstocked tanks like this, it's no different than the LFS who has 10 fish in a 8 gallon aquarium for several months, and they do fine. AS LONG as he has proper filtration, and not more than 1 tang (LOL) then he will MAYBE be fine. Whenever mixing aggressive fish, your best bet is to either add 150 of them, or none of them. If youc hoose the overstocking route, be prepared to treat water often for sickness, and 3x the filtration if not more.
IF he wants to pi$$ his money away, let him do it. It's worked out for me before, and is currently.