bikingshearer 

Those Dura Aced parts are not 1st gen. 1st gen rear derailleur said "Crane," not "Dura Ace," 1st gen shifters did not look like that, 1st gen chainwheels had more metal on them, and 1st gen brake adjusters did not look like that. Not a problem and this does not mean your bike is any better or worse, but it does mean that it likely dates from the late 1970s or maybe very early 1980s and not the mid-1970s when Shimano first put out its Dura Ace line. That rear deralleur was certainly builf before 1984, which is when SunTour's slant pantograph patent expired and Shimano could (and did) copy it, as does everyone else now.

As for issues with Mexican-built Benottos being over-cooked and cracking, that absolutely was an issue back in the day, but I suspect that those frames have self-destructed by now. If it is still riding well, my guess is that it was brazed properly (and not all or even most Mexican Benottos had this problem), regardless of where it was built, and should continue to hold up just fine.