I found #4 on a forum where people discuss kits they are building, and I've been back there and found that #6 was there too, but I completely missed it because I was looking for something else.
This one is a bit confusing. It seems to be an AMT kit, but also has MPC on the box. I think they are both now part of the same company.
Also the car is just referred to as "Can Am" on the box, but it seems that it is actually a model of the Howmet TX MkII. The Howmet TX was an attempt in 1968 to produce a gas turbine powered sports racing car. Two cars were made with enclosed bodies. The second of these was rolled during the 1968 Le Mans race, and was subsequently rebodied as an open top roadster. That's this kit, though the car has subsequently been restored back to its original form.
I don't know if the open version was ever raced, but it was used to set some FIA speed records in 1970.
I haven't found any pictures of the actual car in this form, only the model.
