Youll find that on closed roads its completely different as you can straight line a lot of the corners, and, of course, you dont have to worry about speed limits!!! The Manx Motorcycle club do seem to like you to have some Road racing experience, although when I first entered I only had short circuit experience, and was accepted, so why dont you look at doing some of the other Road races first, like Jurby road etc, for which youll also need a National licence now, I believe.
As you now live on the IOM Im sure there be no shortage of people to turn to for advice. Come on, all you Manxies, give the bloke some help!