The non de plumed racing driver - there should be some great tales.

Baroness Hélène van Zuylen van Nijevelt van de Haar entered the 1898 Paris–Amsterdam–Paris Trail using the pseudonym Snail and became the first woman to compete in an international motor race.

Another reason was surely ease of use - for team management, announcers, programme typesetters etc. For example:

B Bira = Prince Birabongse Bhanudej Bhanuband
JJ Lehto = Jyrki Järvilehto (Imagine Murray Walker getting his tongue around that name)
Johnny Dumfries = John Colum Crichton-Stewart (7th Marquess of Bute)
Alfonzo de Portago = Don Alfonso Cabeza de Vacade y Leighton

Did Umberto Ledfotti really race at Bathurst 12-hour? Surely taking the piss

Of course had Norman Barry racing as Frank Bryan in the Mustang around '67. Were there any others on the local scene? Some may have preferred to be anonymous in hindsight