Actually, they were really wasn’t a “more secure” vehicle...SSX100—or “Queen Mary” wasn’t bullet proof...none of the tops were bulletproof, and Kennedy had been riding around in an open limousine throughout his entire administration...see the pics The Kennedy Detail...
I am sure you are correct.
(my it’s been a long time). I think the original issue was not the safety of the vehicle, but that he shouldn’t even visit Texas and tour around the streets in an open vehicle.