Not the first, i remember a company that sold convertible hardtop conversions for 65-66 mustangs about 15-20 years ago. It was around $10k to get it done, not many were done since most 65-66 stangs were worth less than the conversion cost. It does look like a nice clean conversion on that 5.0 thou.
Wow, I actually like that. Any more pics or info?