There is an article in this months Motorsport magazine (or is it in Octane?) About one of the firms who made the replicas. They started off with a brief to make the BRM for drive-by shots, then had to add interchangeable bodywork for the March and Ligier along with engineering it for full on standing starts. They were given 3 months!
PS: The Ligier bodywork was a compromise because the BRM wheelbase was a lot shorter, so the giant airbox looked ridiculous. They had to reduce it to make it look more in proportion with the rest of the car. I got the impression that the guys who built it were disappointed with the compromise.