AMS.

Given the absolute lack of MK I forends, a modified MKIII forend is the best you are going to do and it is about as correct as you can do for a free state rifle. The free state rifles used MK I forends modified for the MK III rear sight protector and either a modified MK I rear hand guard with the metal removed or a early MK III rear hand guard.

Also all of the CR rifles I have seen that were correct at late MK III rear sight leafs (as your rifle has).