If you want to upgrade your engine, think about basics. Give it a tune up to see its condition. If the condition is fair, then, extractors and a good carburetor will free its potential.
Before going into more modifications to the engine, upgrade your ignition system with a better coil, and the distributor can be upgraded by playing with different springs within your stock distributor.

With extractors, a downdraft Weber and distributor and coil work, you will have a nice swift 120Y.

Before going into more engine work, get a decent suspension, good struts, rear shocks, and you can add blocks or decamber the rear springs and get shorter springs for the front.

There is lots of things that can be done, all in accordance with your budget.