rocker arm bolt (6) loose!!

[Dave]

After loosing almost all of the engines power and having such a rough running engine I thought this was an electrical problem. It turned out to be much more than that after I decided to investigate even more...

I am currently faced with 6 bolts that have stripped out of the rockers that go onto a head of a 1988 mercedes 300e. I have since cleaned everything up . Almost ready to begin my thread repair with the engine and head in car. After having read many previous posts on this subject most of my questions have been answered...those that Im unclear on or am seeking advice on are the following..
1. I am planing on helicoiling all the threads while I'm in there. I found a helicoil that is a selflocking (when a bolt is in place) as opposed to the free standing inserts most parts store sell... has anyone used these???. (I think 12mm length will work better than the 6mm length but will measure first before ordering).. a engineer from an aviation bolt manufacturer told me that these helicoils are better for my application with aluminum since they will insure the threads dont spin out with heat and vibration .yet can be removed if necessary with extraction tool when bolt is removed..

2. Are the torque specs for these rocker arm bolts 15ft/lbs or 13ft/lbs.. i have seen both mentioned in posts..(8mmbolt-1.25 pitch)
I was told that to properly torque these bolts with this insert that I need to add an additional 3-4 foot pounds to over come forces from the expansion ring in this helicoil as the bolts are torqued..so I will be using a torque wrench for shure..

4.Should I have 2 diagonal alignment tube guides per rocker assembly? I need to find a new one, The one currently that is in one of the rockers has its side chipped. Can the one in the Rocker that is chipped be taken out it looks to be a pressed fit? the other two on cylinder #6 are out and loose?

5. Can I still use these bolts if they look visualy ok or can i easily get upgraded bolts mentioned , chromoly I think they were called?

6. Lastly I am planning on using a 21/64 bit . Do I need a short length.. Will I have the space needed with a drill on cylinder #6 and the firewall? Is it ideal to use a 8.25mm bit ?(this is slightly smaller than a 21/64 bit.)

sorry for so many questions I want to take my time and do the strongest best repair my first time with this. Any opinions or tips are appreciated. Dave