Yep, Extractors, Larger valves can be inserted think I fitted toyota crown type, double valve springs, a good cam grind, balance and linish the crank, A decent performance shop can match port the head and cc the combustion chambers. If you want to get carried away you can also get the block decked, go for a decent gasket set and a good set of rings.Redline do intake manifolds for either a single 45DCOE webber or twin 40 DCOE sidedrafts. All these are fairly standard mods. Ditch the mechanical fuel pump and go electric, you can also ditch the belt driven fan and go electric as in such a small motor every bit of power saved is power gained. Carried them out on my 1973 corolla back in the late seventies.
Now I'm showing my age.
Hope this gives you some ideas