I expect that you should get a hold of Bludie Harlaw by Olsen.
It contains the actual contemporary accounts and then goes over all the later bolt on additions lacking in foundation. It is available on Kindle or as a hardback, also on Amazon. Like many other medieval battles, much of what appears in hobby publications about Harlaw is based on the later additions, so this book is a must if you want to recreate it, rather than the Sadler book.
Thank you very much for the info.
I've just ordered the book on Amazon.