Bear in mind I usually build older cars which may or may not have the original strength left in them but I have knowledge of 2 different convertibles that ended up with severe problems while being taken off the frame without doors on them. Bracing is cheap and easy. Even if there is only one chance in 20 of having any issues it is not worth taking that chance. One of them folded in half. BRACE IT. I also recommend doing it in such a way that you can hang the doors and verify gaps as you work.