If you want to go the distance restoring it, I likely have a couple of sporterised #4 lowers that still have the tie plate across the back end. I usually just throw them in to the woodstove, and I think there is one languishing underneath the kindling pile now.
You can use some of the wood to repair the missing portion where the trigger mount went on the mk2. I have seen these repaired over the years as well. Seems like the military would sometimes reverse their misdeeds when required.

Intersting where they installed the splice forward of the screw. Was this a repair of a existing crack, or a preemptive repair of a commonly cracked area?