One of the nicest (non-factory) convertible conversions I ever saw was at an AMC show in Kenosha Wis.
http://www.automotivetraveler.com/in...503&Itemid=166
An engineer created a roadster version of the AMX coupe, and custom made a fully hidden convertible top by modifying a mid 60's Corvette top. It didn't even look bad with the top up. (Something that most aftermarket roadsters never seem to get right).
He welded in boxed steel supports "inside" the rocker panels, and tied them in with steel rebar that he ran through the windshields a-pillar. He then secured everything together using "expanding foam" that turns solid. I think he might have added an X-Brace from the Corvette C4 Roadster. It attaches under the Corvette approximately in the same location our rubber "jack" points are located.
I spoke to him for about 15 minutes, and he assured me the car felt nearly as "stiff" as my coupe, and he noticed no cowl shake at all.
I had a very low mileage 68 AMX with a solid rust free body that needed a complete restoration at the time, and I told him to name him price to create another AMX roadster for me. He said he planned on doing another one for his son first, then he'd think about it.
Well, he passed away not very long after we had that conversation, so needless to say it never happened.