My comments were leaning one way - and you were leaning another... <lmao>
When I first read this thread - when you started it - there's only one thing that went through my mind... He's got a perfectly good rifle (a great rifle!) that fills a role.
Now, he needs to fill another role...
Simple - build another upper. In my mind, there's no way I'd cut down a Super SASS barrel, or change the Armalite upper configuration. That is a great barrel, and a great upper. I'd pick up another barrel, of the proper length (for it's new job). Grab a stripped upper, new BCG - keep a new bolt mated to the new barrel...
Hell, before you know it, you have two capabilities in one rifle - two uppers that do two completely different jobs. One lower in the safe. You can easily transport the second upper with you, where ever you are, even cut foam in a special hard case for it. Two capabilities with you, easily, if you're driving to a location. Switch uppers, change roles.
Now, in practice, that always sounds good. What happens in reality is a different story... You build the second upper, realize that it's SILLY to have an upper sitting in your safe that can only be used if you take another one off, and you build a dedicated LOWER for that "spare upper..." <lmao>
I see your dilemna, brother - been there. From the start of the thread, you were going to sell this whole rifle off and get a new rifle, to change capabilities. My recommendation was going to be WAY different, so I just shut up... <laughs> For now, I'd build another complete upper. As time goes on, I'd let that turn into a complete rifle.
My $0.02. <thumbsup>