GM-GMC: 305cu sparkplug adapter, aluminum cylinder heads, thread repair kits

Question
I recently bought an 1984 GMC 1/2 ton sierra with a 305/350. After getting it home and looking things over a little more throughly I noticed one of the spark plug holes on one of the head had some kind of an adapter onto which the sparkplug was then screwed into. It appears to me that perhaps the thread might have been stripped and had to be enlarged, what looks like an oversized adapter was then used so that an original type sparkplug could then be screwed into the adapter.  Seems to work, the motor runs fine no problems, but I'm wondering how durable this "fix" is? My main concern is whether at sustained hwy driving or pulling a trailer/load it might blow out? Is this something I should be worried about? Other than that the motor runs strong, good compression, etc.. Thanks!

Answer
Helicoils or thread repair kits, if installed correctly are perfectly acceptable.  All engines with aluminum cylinder heads have these installed from the factory.  Like I said, as long as it is installed correctly, they are nothing to worry about.  I have used them quite a few times with no problems.
Hope this helps.