Nice bike - given the "rebuilt" title you indicated, my bet is that it is/was a stock R65 (second front disk brake was an optional dealer accessaory also) that may have been rear-ended or otherwise had a broken rear wheel... someone installed an LS rear wheel (and possibly donor final drive/swingarm) to get her back on the road again. Not too likely that it was an LS as that would have required a wholesale swap of the seat, rear cowling instruments and instrument covers, along with exhaust, front wheel change to snowflake, etc. But, if you post up the frame/engine number we can verify this.
No matter the provenance, it is a nice looking bike!