Originally Posted by mstateglfr

If your '89 420 fits well, I would much rather have a 105 modern drivetrain 420 than a basic aluminum Tiagra bike.
And I could 100% update an old 420 for less than money than a new Tiagra road bike. The wheels would be nicer than what came on the Tiagra too.

So a higher level drivetrain and nicer wheels for less.
An innicycle headset would eliminate the common cockpit conversion issue of updating older road frames too.

As for weight, a Tiagra drivetrain Trek Domane weighs 23# in a medium size. It also costs $1800. Again, 23# for this bike. I would not worry about the weight of a Trek 420 frame.
https://www.trekbikes.com/us/en_US/b...-disc/p/33085/