Pre 8/1 AR - new resident

Throwaway account because I am slightly concerned I received inaccurate info from my firearms instructor.

I moved to Massachusetts in March 2024 from Missouri. I got my unrestricted LTC later in June. I have an AR that met the feature restrictions (fixed stock, no flash hider, maglock, etc). I was told to make it compliant for Massachusetts. My firearms instructor said that as long as I have an LTC and the compliant firearm in my possession on 8/1, it's legal.

Massachusetts makes the laws so damn hard to understand. Can I own this legally? Do I have to keep it in the lame restricted way with the feature restrictions or should I get rid of it entirely?

Thank you.