[ Usually the main problem with bolts once they are initially torqued down is they never really retain their ability to hold the torque value and they keep stretching out so the head may have loosened up over time allowing for the failure(s). ]

I'm with you on that, and several other old timers in our shop have that same opinion.
One of my co-workers builds race engines in his side business and he flat out says that the "torque to yield" head bolts ARE the reason this engine continues to give head gasket problems.
In fact, this mechanic is now checking his sources to determine if a set of HEAD STUDS are available that could replace the torque to yield bolts. The studs (his preferred fasteners for heads on the race engines the builds) come from ARP.
When I began discussing this engine and its history with him last week I learned that he also uses head gaskets from Cometic.

The head bolts have been replaced with new ones each time the head was off.

I'm not really well versed on any possible automotive renditions of this engine that have been marketed here in the US.
In 2012 when the head was off, I dug around on the internet looking for info of potential parts sources and from what I could gather, this 1.6 engine was used in European marketed GM cars and derivatives, but I did not get any impression that it had been used in the US except for industrial and marine applications.
The cool response I got from our local engine parts warehouse did not sound like the engine was on their radar as a potential profit maker.
As engines come and go through the years, I doubt anyone will ever sigh and wistfully say " Now, that little GM 1.6 Vortec sure was a good engine."

Anyhow, this saga is still unfolding and I have no idea yet what fate awaits the old engine.
I will continue to update.