May I add that I tried this, and there is a small problem you will encounter.
The larger island isn't as big as you think it is. To make this island seem big, BI scaled all the units to a different size. All soldiers, vehicles and buildings. Your map will have a similar template, but a lot of buildings might overlap, or be to short and leave gaps.
I ended up just opening up OFP and then opening up ArmA and making a similar template of the map from scratch, then using OFP I visually fixed everything until it was right. Took a while though.