In my experience, the worst 10/22's were like this:
Barrels were absolute crap in 1988-2005/6 production,
receivers were sloppy always up to 2004-2005
(but material-wise, all cast receivers have good aluminum),
bolts were sh!tty after very early 70's,
aluminum trigger group housings were lower quality after 85-88,
regular stocks were always like pressed sawdust.
Mags were always great.
Regardless of what you read on internet,
the new plastic TG housing is the best option (for now) if
you want to do a quality custom-built TG.
On a different subject, no matter what is changed,
even if it doesn't have a single rugar part,
if it can take the original rotary mag, it is still considered to be a 10/22.