I bought a gen 1 Hunter too....I wanted a rifle that had a normal rail height, FA and dust cover, rifle length gas system....the Hunter fit the bill....I think your budget is pretty important to know for good answers. Since you didn't buy a SASS or Recon to start with, I take it you have a budget in mind. And you won't lose much going from 20" to 18"... You might be better off setting that upper aside as a spare and just building a new upper the way you want it instead of wasting your 20" barrel.
I topped mine with a PEPR mount and a Primary Arms mil-dot 4-16x44 (illuminated).
I have no plans to modify the rifle but I am kind of kicking around getting a second upper or a second rifle....and I'm not sure why.. My issues so far has been finding what load it likes in the 165 to 178 range.... My goal is sub-MOA.. No joy so far. My dad just gave me a pound of Varget so that will be my next set of loads. Also, the trigger seemed a little gritty since I bought it. I pulled it out last week and just cleaned up the surfaces with a tooth brush and stone. Felt better when I re-installed it, could be my imagination but I'll see next time I take it out...
Tag for interest....