Somebody needs glasses. The name on the forks is Ishiwata . Ishiwata was bankrupted in 1990 but the manufacturing has continued as Kaisei tubing and is still available.
Xlobsterman
This frame and packaging is a Museum piece. Excellent reference for those wishing to restore another frame as I am. Frame it in a glass box and hang it on the wall, you very lucky man. Does the seller have knowledge when the shop received it or how long it was in the store.
Know it is not a Bridgestone manufacture, just search Bridgestone Serial numbers and the number is no match. Bridgestone use either a number then letter, ie 5A or a letter then number, ie A5 never two letters as BS. This was to define which of their factories made the frame. Just do a google search for Bridgestone.
As is said my frame also has BS367823 and I have seen a few starting with BS but also other letters as below.
BS357553
BS367578 BS 367641 for this frame
BS367823
BS367845
BS440296
CS472494
CS476244
KS314155
Thus another reason why Bridgestone does not apply by referring to BS when CS and KS are to be seen.
In respect to 1983, the numbers above show a different picture.
The Serial number with the month letters B,C and K indicate something else. The second letter a year as per the Schwinn Chicago format doe indicate 1981 and these frames compare with Specialized 1982 lugged frames and other lugged frames of the period early 1980s. The serial number increase except for KS314155 does show an alignment with one year of manufacture with 6 numbers being applied as Schwinn had in the 80s.
We definitely need a Schwinn employee of the early 1980s to put in a comment.
Does 30 on the end of the box indicate one of 30 made.