I own an 89 Trek 520. it is still used today for gen fitness riding and for short touring. The frame show no signs of giving it up. The bike is still equipped with it's original drivetrain -still going strong. Even i'm surprised, but if it ain't broke...

I also own a 2004 520. That too is a great bike and going strong. Realitive to the 2014 520 it has higher level components. For that reason I'm not a big fan of the new 520. If given the choice i'd build up the old frame with the level of components that will serve your needs, rather than the grab bag Trek has used to hold a price point. Not that there is anything wrong with a 2014, 520, only that for the $1300 or so one will set you back, that money will buy you a higher level bike on a build up.

If the frame is solid you have nothing to fear.

Differences would be that the 89 will have more flex than a new frame. That is not a deal killer. the 89 is not flexi! Just not as stiff as the newer frames.

The 89 took 27 inch wheels and tires. The brakes, I think are the same on both my 520s, gotta look again to be sure.

There are as many brazons on the 89 as on the 04.

There was book written about five years ago about a guy who dusted off his 25 year old touring bike for another big ride. The bike was an 1985 Trek 520. The bike went 2000 miles with little more than a tune up and new tires.

So, the bike is up to the challenge.