you'll need new bars to go along with this new stem and threadless adaptor.

my advice: put no money into that bike other than consumables (bar tape, chain lube, tubes, tires). save your money for the next thing. if there is no next thing, it's not because of that bike.

people can get hooked on vintage-- start a lifetime of cycling-- but you shouldn't be trying to modernize vintage. that just doesn't make sense.