Chipperdog,
I have a 1999 2530 DV with a single bracket. I originally had an OX66 250 HP as well. When I decided to repower, I also looked at changing over to twins. When looking at the cost of twin 4 strokes, I still thought I could afford it. But then I looked at the cost of the twin bracket purchase and installation, rigging, and additional gauges. I also realized that there are a bunch of differences between the older 2530s and the newer ones. And some only have a 154 gallon fuel tank in comparison to the newer 173 gallon tanks. I would have really liked to have an extra 150 HP but this is the configuration that I bought. Call the factory and see what they say about the bracket. Make sure you try and anticipate the hidden costs (gauges, controls, cables, labor, labor, and don’t forget the labor!). I decided to stay with the original bracket and went with an F250. It’s a little slower but my efficiency increased tremendously. If you stay with the single bracket, you may be limited to the F250. I'm not sure of the dimensions of the new V6 F300. Unfortunately, my bracket won't handle the V8 F350. Not only is the HP rating too high, but also the dimensions of the engine make it too large. The bracket is too short for the height of the engine cover.
Good luck with your decision.