Lori:
I have a 1995 208 as well. Love it. I'm considering a 4stroke repower and doing a little research.
My original 1995 Evinrude OceanPro still runs like a champ but I have three young kids and continued reliability has become an issue. I'm looking at the Yamaha F200.
Several factors to consider as well as my unprofessional opinion:
I think a 250 anything is overkill for a 208. In reading the previous post the term "fly" comes to mind. I think that may, in fact, become a reality for you with all of those horses combined with all of that extra weight.
When these boats were originally designed, most of the 2s motors on them weighed less than 400 lbs.
My Evinrude OceanPro 175 weighs 370lbs. The F250 you are considering weighs 604 lbs at a minimum and probably closer to 618 lbs. That's a huge difference.
The F200 weighs in at 583 lbs. Still, a huge jump from 370 lbs.
We're doing a little experiment this weekend with ours. We're going to have a 210 lb friend of mine sit on top of the Evinrude OceanPro and see where the scuppers end up. If the scupper drains are at or below the waterline, with just the 210 lb friend atop the motor then, we'll have to look at other options for a repower. That will be the tell all that it's just too darn heavy.
If the drains are too close or below the waterline with the just the added weight of an F200, it will simply be too much weight. Add full fuel, bait, gear, beer, food, cooler full of fish plus some friends or family to share all of that with and it's my opinion that you'll be asking for trouble. Especialy if you have 210 lb friends like I do.
The newer boats are being designed a little differently and I hear that Grady is moving the batteries forward and other tricks to compensate for the added weight of the new 4s's. Yours may be ok but I would definitely be on the lookout.
I think adding ballast forward is a horrible idea. However, we need some input from more nautically technical minds than I.
I'd have the dealer/seller put that boat in the water with the F250, full tank of gas and a couple of friends. See for yourself. Take some pics of the transom at the waterline and SHARE!
However simple our test is, it's the best determining factor that I could come up with and it's also received the seal of approval from the folks at Grady White. I'll post the results once the tests have been verified.
I'd certainly welcome other opinions and will look forward to much stimulating conversation on the matter. If I was an expert, I wouldn't need this terrific forum. It's a great place to listen and learn.
Happy New Year.
Steve