unworthy1

I had limited time so only took these snaps of the serial numbers/letters on BB shell
But short story is I found an abandoned aluminum frame and CF fork with 105 cranks, SR pedals, rusted KMC chain and loose front wheel everything heavily spray-bombed black (together with street homeless belongings swept into a pile awaiting the trash collector, no persons in sight...commonplace on the streets of SF these days).
So I rescued it from the dump.
It's an AL road frame tig-welded with a "fat-blade" CF fork with threadless AL 1-1/8"steerer, the BB unit is a Shimano hollowtech and the 105 crank had single 42t chainring. It still has a RD hanger.
One side of BB shell says:
PR-SL1-5X (possibly X= "6" which is probably correct for size it's about a 56cm), other side has:
U21180322
Any guesses from our serial number experts as to the make (@T-Mar)?
My plan is to clean up and remove the paint, offer it up to co-worker or donate to one of the local co-ops

T-Mar

U-code format is consistent with that believed to be China Bicycle Company. If so, it's from November of a year ending in 2. Narrow the decade down based on the component codes. CBC was the company that bought WSI in late 1989 to fill their factories, so the leading candidate would be a Diamondback, though they also did contract manufacturing.

unworthy1

Many thanks, T-Mar!