The VMCC Closed Roads Parade is part of the VMCC Manx Rally programme. You can find the details here:

http://www.vmcciom.org/

I took part in 2012 on my Laverda 750GTL and had an absolute blast, despite the wet and cold weather with fog on the mountain section. It is speed controlled in that you are released from the start line in batches behind a travelling marshal. But they get a fair old lick on, and it's just a joy to ride a lap without traffic lights or oncoming traffic. Stick a go-pro on your bars to record it and you'll have something to remember for the rest of your life. It's fantastic!