With permission from the owner of the Spirit of Speed licence, John Jones-Steel, please find you a 3GB archive from the studio Broadsword Interactive containing Game Design or promotional documents, a lot of assets (maybe the one for cancelled tracks), development tools (level editor etc.), source codes and much more...
Many thanks to John Jones-Steele for his generosity.
His development studio: https://west-coast.wales
Please note that the assets cannot be used in any commercial game. The cars in particular were licensed from Mercedes, Alfa Romeo, etc. They could only be used in Spirit of Speed, because they wanted to support a small independent Welsh company!
To download and read below: