I will only add that, you asked about "upgrades". Or, was it original equipment? Or maybe both.
As Chas stated, the front derailleur probably broke. They tended to do that. Though some turn up their noses at the Delrin derailleurs, they worked quite well when new. I know Bigchainring agrees with me that they're OK. That rear could perform just fine, if it hasn't got a whole lot of miles on it. Take it apart, clean and lube it, and see how it shifts.
If you decide to upgrade, my only admonition is please don't do as many did back in the day and alter the dropout hanger to accept other derailleurs. Look for an all metal Simplex derailleur that will fit the hanger.