I'm not sure about using sub frame connectors to fix a door gap issue, but convertibles gotta have them. I've owned a C body convertible and a B body convertible and both felt like putting 4 wheels on a Slinky without connectors. Without subframe connectors, the door gap changing when jacking the car is normal convertible behavior in my experience. I would check the underside of your car for signs of a tweaked or sagging chassis before adding the connectors.