The first issue in 1960 was the impressive Chevrolet Impala in sedan form in January as catalogue number 220. The State Patrol edition had been issued at the end of 1959 so this was not the first time people would have seen the Impala although I suspect that in most shops this and the 223 State Patrol may have arrived at the same time.
The first models would appear to have been the salmon colour and the blue model with a lemon interior and they would have had smooth fixed wheels. They would also have had the base type as shown in the centre of the illustration below. Later, models with shaped wheels and, towards the end of production and somewhat scarcer, with free spinning wheels will come along and, at some point in the fixed wheel period, with the different base.
I have also noticed a slight variation in the plastic interior piece. It appears to fill the space available better in the middle one shown here. At the rear edge there also appears to be a gap at the corners on the later models.
This will prove to be a very popular and long-running model, to be revived in 1965 when someone slices the casting in two and inserts a chrome section which makes four new and still impressive models.
The chart above shows how I have found the various Impala editions spread with regard to wheel types over the years.