As a RF and comms savvy guy, and Ham operator, I could help you some I think.
First off, don't know what's up with that path calculator you used. It seems too optmistic and forgets to include curvature of the earth? This one gives a more expected answer, but if only 300 ft and 200ft on each side, your looking at 21 miles unobstructed.
Edit: I'm sorry I was so quick to disparage the Heywhatsthat path profiler, very good tool. But, you picked "flat earth" instead of include curvature.
http://hamuniverse.com/lineofsightcalculator.html
Now, that's not to say you can get farther due to diffraction, or atmospheric ducting, but you'd be at the mercy of changing conditions. Are there any mountains near the prospective link areas?
Edit: I see islands inbetween, how high do they get at their peaks? Unless you have 3000-4000' mountains at the shores of PR and DR, you aren't going to make it in one hop. Multiple hops may be your only choice.
Basically, you need high locatons that would provide you with line of sight, good high gain directional antennas like dishes or many element yagis, and probably radios that have a fair amount of power. Though you can cross 60-100mi with a watt or less, especially with good antennas helping.
Being legal with this could be a challenge. You'd want to talk with officials on what you could do on which bands. Maybe get an emergency waiver from both governments?
You might want to look at what these guys are doing. You'll have to dig around a bit, dig up a powerpoint or video maybe, but the info is in there on off the shelf router and other radio link hardware with good dish antennas for long links. https://www.aredn.org/ They are creating high speed mesh network links out of off the shelf hardware. Interestingly, they based their firmware off OpenWRT...
They are designed to be a Amateur Radio (Ham) setup, using Ham frequencies. You would need to be licenced, and would be limited in what you could send. You may be able to use the radios on public frequencies, with power restrictions, and not be as limited. Also, possibly an emergency exemption from the gov's might be available.
Let me know what questions you might have.. would love to help over there...