No time for a lengthy response, but my LLD is 3 cm following a serious bicycle accident. You need to ring up Tom Slocum at High Sierra Cycling. While the custom 'systems' he builds are not cheap (he calls them systems not crank sets), it was the only way I could ride again without pain. My crank arms are 165mm (sized for my short leg), but then the crank arm on my longer leg side has a dropped pedal that rotates throughout the pedal stroke. The chain rings are also elliptical and off set, to balance the leverage and be gentler on my knees. His work isn't cheap, but its right on. I did have to fly to california for a personal fitting, but it was worth every penny.