Bad idea, especially if the boat has an inboard. That sounds like an awful amount of weight to add off the stern of that boat. The hits against this configuration include:
1. unbalancing the boat
2. loss of prop wash control
3. prop popping out of rough water
If this boat has an inboard, I would expect that when you go to sell it, any buyer will still hit you with the cost of an inboard replacement, the outboard being lost money and junked
Certified...in several regards...