Ok, you have a few things going on here so let’s address each.
1. You can buy an upper, or build/change your barrel ( not sure what an extended rifle gas tube is) but I don’t think you’re addressing your main problem. You are looking to hit the ten ring, with solid groupings, consistently correct? Not knowing you or how you targets are looking at the range (you have not posted any pictures) but how are your fundamentals? Are you consistent shooting with your set up now? Groups generally in the same spot? Tight or loose? What FCG is in the rifle? I find that this is usually the first and most useful thing to change.
2. Scopes. The better the scope quality, higher magnification and mount quality will result in repeated shot impact points. Again grouping is more on your end but these keep it consistent.
3. Familiarity with the platform eliminates this. There are fully ambidextrous lowers out there, I like MEGA MATEN personally, but you get used to it with repetition. If you are shooting for groups this isn’t even a factor. More of a defense/drills issue which will resolve itself through repeated use.
Can you state your specific goals you are looking to achieve? How about a general budget? Maybe what you dislike the most also as there is a lot of people here with varying tastes who have tried a wide variety of options on these