I had a similar situation, only in reverse order. Mine came with a set of target grips and I still wanted the original factory grips. I contacted the seller and he looked through his "stuff" and found a set of factory grips, and shipped them to me. All it cost, was the mailing. ......They just fill the hand better.
Fixed sight version would have been the "Service Six". Everything is the same as the Security Six but with fixed sights.I had one with fixed sights in 1976. I still lament selling it