Hello and welcome Nathan.
The Parnell book is great if you are interested in purchasing a UK built Cooper/Coper S. It will get very confusing though if you are a beginner referencing Parnells book against the Aussie Cooper S. It leads to a plethora of misconceptions.
I recommend buying issues 1 and 14 of The Mini Experience Magazine
http://miniexperience.com.au. Issue 1 compares an Aussie MK1 S to a UK MK1 S. All be it, the Aussie MK1 S featured in the magazine is an early production example so it has differences compared to the majority of MK1's built. Issue 14 features the 1969 Aussie MK2 S, again a production period that can vary in its specification. It also has general info on both the Aussie MK1 S and Aussie MK2 S regarding ID info.
If you are seriously considering purchasing a particular car, I would also recommend taking along with you someone experienced in identifying these cars. There are many on this forum that would be willing to help you out.
PS: Your friends car would need to be a UK production if its a true Cooper S as Aussie production only started in 1965.
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In the garage:
1970 Morris Cooper S MK2 | 2010 MINI Cooper JCW Challenge Edition

Now with new owners:
1964 Morris 850 Van | 1965 Morris Cooper S MK1 | 1976 Leyland Mini | 1999 Rover Mini Cooper Classic | 2006 MINI Cooper JCW