Peter O'Toole was about a foot taller than the real T. E. Lawrence (1888-1935). But then, someone of the statue of "little Lawrence" wouldn't have made much of a film hero.
For dramatic convenience, some of the film's characters are composites. Alec Guinness's character is drawn from both Hussein bin Ali, the Sherif of Mecca, and his son Prince Feisal (1885-1933) for whose portrayal he was far too old (at 48) since Feisal was just a couple of years older than Lawrence (only 30 at the end of the war). The Arab Bureau's Mr Dryden - played by Claude Rains - is a conflation of many real persons.
The fictional journalist Jackson Bentley - played by George Kennedy - is based loosely on Lowell Thomas (who met Lawrence for the first time in a Jerusalem hotel and was never present during any of his military escapades).
There was a real Auda Abu Tayi (Anthony Quinn) but not a Sherif Ali (Omar Sharif).
General Allenby's Cairo headquarters were actually located in a belle époque hotel quite unlike the 1930s Moorish fantasy depicted in the film.