The Centurion brand was created when a bicycle sales agent, Mitchel Weiner, got involved in a Raleigh project to develop a Japanese version of the Grand Prix in 1969. Raleigh backed out of the deal and Weiner was stuck with 2000 Grand Prix clones which he labeled as Centurion and made a handsome profit selling them in California. Centurion was distributed though his company, Western States Imports, and was a very popular road bicycle brand through the 1980s. In 1978, the company started the Diamond Back brand for their BMX bicycles and later applied it to their ATBs. 1989 was unprofitable and Mitchel sold his stake in the company. This was also the last year for Centurion in the US, as the new owners consolidated all the models under the Diamond back brand, though Centurion continues in Europe to this day.

Weiner had success using a clone of the Grand Prix and obviously decided to clone a Cinelli for his top end model. A similar approach was used by Windsor for their Mexican manfactured Professional. I'm not sure of the exact production dates for the Professionals but the newest sample I've seen is from 1980 and they were certainly gone by 1983, having been replaced by the Turbo. The North Star head badge is typical of late 1970s models, so I suspect that is also the era of your friend's, though the serial number will provide a definitive answer. The tubing is Tange butted CrMo, though it is unclear which grade. Period literature does not specify the grade and decals ,when still present, tend to be generic. Regardless, the the samples I've seen tend to be well designed and manufactured.