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Progressive is the brand name. The most popular shock for a mid 70's Shovel is the Progressive 412's in 12 inch. You can go lower but the ride will suffer. They are around 200 bucks. A cheap asain copy can be had on ebay for about 80 bucks. Honestly, they are almost as good as the 412's progressive makes. I've run both on my Shovel and prefer the progressives.