The earliest BICs were the 980 and 060 in 1974, then the 940 in 1975, then the 1000 and 920 in 1977. I'm not sure about the 981 but it may have been that year, too. The VIA series next and finally, the Z series in 1980. They all had the same basic mechanism, packaged differently or with the more expensive models featuring electronic control.
In my opinion, the 1000 is the ultimate but they are all good and, as Bruno said, underrated. Some may consider the top models of the VIA or Z series, with digital speed and time elapsed readouts, the ultimate.
To find out if the belt is still available, contact Adam at Turntable Experts, A.K.A. South Street Service in New York. There may be two belts involved. I can't remember. Also, Turntable Needles/Belts sells round belts and you may be able to measure your current one, if it's broken, and order a suitable replacement from them.
Doug