It won't matter one bit the stainless helicoil in aluminum.
Helicoils are okay,but I like King serts and Threadlock inserts better since both are soild and not a coil spring.The one drawback they have is they require more metal around the hole.
As for Helicoil instalation,it's pretty straight forward,just buy the kit and follow the instructions.
The old nut on the backside trick was fine,it's the way things used to be made before "cheaper" took over for "better".
I just need one more tool,just one!