Gary are the dimensions even remotely similar? I mean width, shape of windshield header, side window opening, etc. Being aluminium, I'd hate to see you hack up a perfectly good Alpine removable hardtop.
I always thought the C1 (53 thru 62) Vette roof would make an excellent starting point for a XF roadster roof. But unfortunately they're in short supply as well.
I knew a guy who would fabricate large body panel molds using huge blocks of styrofoam. He said he would take all the measurements he needed, then he would use an electric carving knife to cut off everything that didn't look like the part he was trying to build. Then use sheets of fiberglass and resin to build up the part.
I think the easiest way to do a mock up for a fiberglass mold, would be to use an existing XF convertible top, and then just smooth out the ribs that show thru the top.
Here's a thread I started awhile back
https://www.crossfireforum.org/forum...e-hardtop.html.