The 54000008 are standard ride height and are listed for bikes as old as 09, The 54000159 are lowered and are listed only for 16,17&18 bikes
spend a little more and buy Ohlins,or Pro Action ..
Ohlins and Pro-Action are great shocks. If they are out of your budget range check out Progressive Suspension. Progressive has products that are far better than anything Harley sells for the same or less money than Harley asks. I'm running Progressive 444 shocks and I think they are great. If you want a lower ride look at their 944 series.
For a little over $500 you can get a base Ohlins or Bitubo..I chose Ohlins that I got from Motorcycle Metal, a vendor here. Bitubo are also available from DK Custom a vendor here...
I put the pro action on my 2018 street glide and they are absolutely worth it. If possible I wouldn’t spend money on Harley shocks when the aftermarket options are so far beyond them.