There were 2 iterations of electro-forged frame bikes named "Sprint" and built in Chicago.
The first and best of these was the version with the short-coupled (aka bent-tube) frame, which was built from 1974 through '77. The frame included a labor intensive hand fillet-brazed bottom bracket with the kickstand tube brazed on the underside. The frame geometry changed to an even shorter wheelbase and 1" shorter top tube for 1975 and later, making those versions even more responsive.
The 1974 and '75 models were equipped identically to the Continental those years except for the saddle, which was the lighter weight unit from the Le Tour. Even though they were not in the catalogs after '75, in 1976 Schwinn announced to its dealers that it had sufficient components to build an additional 1,500 Sprints (680 22" frame and 820 24" frame, models 422 and 424 respectively). The '76 and '77 Sprints were equipped the same as the '76 Continental and '77 Sierra (in '77 the Continental was renamed Sierra) respectively, except the Sprint had a painted fork with a chromed cap on the crown, while the Continental and Sierra forks were fully chromed.
The Sprint name was then re-introduced in the Spring of '78 as a new "low-priced" model between the Sportabout and Varsity. That version had the same frame as the standard Varsity/Continental.
That appears to be a 1974 Sprint with a BK (Feb. '74) frame serial. That was the only year they were available in Opaque Blue. The fenders were an add-on, it did not come from the factory with them. I wonder if that frame and fenders were from the bike seen here:
http://www.schwinnbikeforum.com/index.php?topic=19038.0
I'd pay up to $100 for the lot. Note that is the larger 24" frame size. Check to see if there were any holes drilled in the BB shell to mount the fender.
