Rather than treating the symptom by going to an offset upper cross shaft, why not have the root of the problem fixed and have your frame rolled? Over the years, the front frame sags and the upper control arm mounting points slowly move inwards, which as you know leads to the alignment shop running out of shims.
Having your frame rolled will cost about $250-300, and will fix the root of your problem. You usually don't even have to remove anything more than the wheels to get it done. They chain down the outer "ears" of the frame near the shocks, and push up with a ram under the crossmember, which rolls the ears back outwards.
Offset cross shafts will get you by for now, but sooner or later the frame will sag to the point where even the offsets won't be good enough and you'll have to roll the frame. It's up to you, but I would have the frame rolled. Just find a good, reputable shop. A good shop can do the job in about 2 hours.