The Issue:
From Wikipedia: Gautama Buddha:
The times of Gautama’s birth and death are uncertain. Most historians in the early 20th century dated his lifetime as c. 563 BCE to 483 BCE. Within the Eastern Buddhist tradition of China, Vietnam, Korea and Japan, the traditional date for the death of the Buddha was 949 B.C. According to the Ka-tan system of time calculation in the Kalachakra tradition, Buddha is believed to have died about 833 BCE. More recently his death is dated later, between 411 and 400 BCE, while at a symposium on this question held in 1988, the majority of those who presented definite opinions gave dates within 20 years either side of 400 BCE for the Buddha’s death. These alternative chronologies, however, have not been accepted by all historians.
From The Urantia Book:
(94:7.1) Contemporary with Lao-tse and Confucius in China, another great teacher of truth arose in India. Gautama Siddhartha was born in the sixth century before Christ in the north Indian province of Nepal. His followers later made it appear that he was the son of a fabulously wealthy ruler, but, in truth, he was the heir apparent to the throne of a petty chieftain who ruled by sufferance over a small and secluded mountain valley in the southern Himalayas.
Related research:
Confucius lived from 551–479 BCE.
UPI, Science News 2013 article on a discovery that support the time period mentioned in The Urantia Book:
Nov. 25 (UPI) — Archaeologists have uncovered a Buddhist structure below the main shrine of the Maya Devi Temple in Lumbini, Nepal. The discovery at the legendary site now puts the birth of Buddha at 550 BCE, nearly a hundred years earlier than previously agreed by scholars. The international team of archaeologists excavated postholes showing a wooden railing, and found an older wooden structure below the more recent brick structure of the Buddhist temple.
“What we have got is the earliest Buddhist shrine in the world,” said lead author and archaeologist Robin Coningham of Durham University. “The big debate has been about when the Buddha lived and now we have a shrine structure pointing to the sixth century B.C.”
Expansive Buddha Weekly article related to the discovery.
Times of India article on the 2013 discovery.