73 318 upgrade questions

Have '73 Swinger 318 904 3 speed 8.25 rear end. Holley Street Avenger 4bbl carb.

In the next few months I am looking at an upgrade. Starting with stock heads cleaned and rebuilt and adding headers. Not looking to blow the doors of things out the gate, but a hwy cruiser. What parts would you change? I am looking at cam, timing chain and gears, valves and springs.

Thanks.