I put B&M 250's on my last boat and had no problems at all. I had about 75 hours on the 454 mags when I did the install. I put more than 100 hours on the engines with blowers before I sold it. I haven't heard from the guy that bought the boat, so I assume it ran fine.
How many hours are on your engines? If you already have a lot of hours, it may cause problems, if you don't freshen the engines.