I've had some 6'+ people in my MR2s no problem, but it may depend both on body shape as well as raw height. They're really not that tight a fit, especially compared to, say, a Miata or MGB. If you're really worried about it, go find one to sit in and make your dad come with you (if you expect you'll end up with a similar body style). Should give you an idea.
If all else fails, make sure you get one with t-tops and never put them in