I think you misdated some components. Indexed SunTour derailleurs were introduced in 1987. The Alpha models were 1987-1988. Going on that, I found specs for a Bridgestone 550 in a 1987 Bicycling magazine. It had Alpha 5000 derailleurs and Tange Infinity CrMo tubing. Given that model 450 is lower than 550 and Alpha 3000 was a notch below 5000, your bicycle was proably one model below this. The model 550 sold for $500 US, so yours was likely in the $400-450 range.
Bridgestone was a reputable Japanese company that built good value bicycles. During the 1970s boom, they produced C.Itoh and Kabuki brands. My first exposure to the Bridgestone brand was in the late 1970s. In the late '80s and earlier '90s Grant Petersen designed some some very popular bicycles for Bridgestone USA. See
http://www.sheldonbrown.com/japan.html#bridgestone