Hi, if the sprints are going to be under MSA rules then the roll bar has to be a specific height above your helmet. A straight line from the nose of the bonnet to the roller above your head with the required clearance to your helmet. I would check the MSA regs. There are roll bars around with a removable race hoop and one for road use which accommodates the hood. I stopped hillclimbing in an MR2 this year and there were all sorts of discussions at the last few meetings around rule changes requiring open cars to have even more crash protection, so it is worth checking it out.
