There is no problem at all. Other than the fact that you won't have any gauges, and that doesn't bother you, you'll be fine. The engine doesn't rely on the gauges, the gauges rely on the engine...
In respect to your second question, the only issues you might have with re-powering would be a tach that might have "System Check" in the face, like OMC or Suzuki, and the trim gauge. Merc and OMC trim gauges are total opposites, and one can't be "converted" to fit the other. But who needs a trim gauge? Trim by feel, and if you need to SEE where the motor is, turn around! The rest, i.e. voltmeter, fuel, water pressure, are pretty much good across the board...except for water pressure. Some builders use 0-30 PSI, some 0-45 PSI. An easy google search will tell you what the motor you want to repower with needs...
