One potential issue with adding spacers under the cleat or in the shoe forefoot area is that while it reduces the pedal to saddle distance for the shorter leg when crank is vertically down, when the crank is at the top your foot is that much higher, so the angles at the knee and hip are more acute, which you may not want. Consider instead using, instead of spacers, a shorter crank just on the short leg side. So you could get 2.5mm (or 5 if you wanted) reduction in pedal to saddle distance, but at top of the stroke there is also the same distance reduction, and less acute knee and hip angles. I think this may also help with your foot length difference, as when crank is at 90 degrees forward, it is again 2.5 mm closer to the bottom bracket. I think that helps, but trying to work it out makes my brain hurt!! Ultimately you may find your fit is a compromise between the two legs, neither side can have a 'perfect' fit, but you can seek a middle way to maximise power delivery but minimise risk of knee pain. After a femur break I have quite a large leg length discrepancy, which we can only partially compensate for, and I have just cycled 60miles a day for 35 days across Europe with both 3mm of spacers and a 2.5mm shorter crank on the same side.