“Speaking of the aluminum top frame, is there a best practice for bending the two lips needed for the cabrio top latches?”
I don’t know if it is a best practice, but it requires three pair of electrical pliers.
Decide where you want your latch(es) to be and how wide you want the lip to be. Mark the inside lip of the top frame where the ends of the lips will be. Apply a couple of layers of electrical tape to the jaws of the electrical pliers and then attach a pair of electrical pliers to the frame at the ends of the proposed lip. Using the third pair of electrical pliers, attach to the lip area and while your assistant is holding the frame steady with their pliers, gently bend the lip up in small increments across the width for an even gap of 1/8” - 3/16”
Done.