I haven't seen a beetle in an Avis fleet in probably 10+ months, except 1 in IAH a few weeks ago. Camaros are also not as common anymore, so I'd say it's likely you'll get the Mustang. And most would agree neither are "or similar" to the GT. Further, with a ressie for a GT, you should get it, if there's one on the lot. However, it's difficult to guarantee a specific model (if the one scheduled to come back is in an accident or they don't return it on time, you're out of luck).