You should talk to convertible-conversions.com. They have been at this with E bodies for years, and it is not a project to be undertaken lightly. Just accumulating all the hardware can cost (well) upwards of $10K, and this is for rough stuff. Last 3 pc stainless trim I saw for the top well alone was almost a grand, and you have the windshield surround, belt trim, interior panels, etc to find also. Clips for the holding the trim to the top well pinch weld are virtually unobtainable, I gave $600 on eBay for a set and haven't seen any more since. All body areas where the convertible is different need to be addressed, A pillar posts, rear quarters, dutchman panel, etc.
The biggest issue is the rocker boxes on E body verts are different - double wall construction. These come up on this board and eBay infrequently, but can be had. Without these plus subframe connectors, or tucking a full chassis (like Art Morrison) under it, an Ebody will fold like a bad poker hand..
