Hurrah! At last. Yes, Boom made two of these Sevens in 1990-91 with the serious intention of producing them, but the cars generated very little public interest, so they dropped the idea and focused on building their trikes instead.
Boon printed a sales leaflet on the Seven at the time, and also highlighted the cars in their literature and website last year when they celebrated their 20th anniversary. I took the photo from a sales brochure.
Well done Wendax!