Your biggest issue will be the weight of the engines. Twin 250 V's are almost 1400 lbs. whereas something like twin '89 Yamaha 200s was only about 780 lbs. That will definiltey have a negative impact on the way the boat sits and performs. If you do it, structurally she will need to be better than new. Plan on an overbuilt transom tied to the stringer grid with huge knees, a custom bracket with the biggest flotation chamber humanly possible and the best stern lifting props you can find.
Secondly, insurance companies won't be anxious to write you a policy. I previously had twin 225s on a '93 Sailfish. I was able to get a policy w/out issue, but then again, I was only 50 HP over the max. I inquired about going to 250s, but was told "no guarantees".
Check w/ your local marine police and USCG about the ramifications of exceeding what's listed on your capacity plate. In MD, the CG doesn't care about HP and the NRP (Natural Resources Police) goes by what the CG does. I originally thought I could get a replacment plate w/ an updated HP rating, but that turned out to be false. Was a non issue because I didn't need it anyway.
You also have to think about resale on an overpowered boat. If you plan to keep it until it falls apart, this won't be an issue. But if you go to sell, perspective buyers will be wary no matter what you tell them.
I wasn't able to sell mine in an overpowered state. But I think a lot of that had to do with another factor that has not been mentioned here. So, I sold the 225s and am now in the process of repowering w/200s. Had I known I was going to be selling 3 years after buying, I doubt I would have bought the overpowered boat. But my original plans were to keep the boat 10+ years and repower somewhere in that 10 years with 200s, run it a few more years and then sell.
Ultimately, it's your boat. So, I say go for it if you want. Mine ran awesome w/ the 225s, so your's will be an absolute rocket. The motors should fit on the bracket (again, I wouldn't recommend the factory bracket though), but I have no clue what's involved in rigging them. They are DTS w/ power steering, right?
Why not trade them in on a set of 200 Optis?