" Speed cost money, how fast do you want to go?"
That's been true since the first hop-up part was made, and still true today. A lot depends on what your goal really is.... a hill-climber, vintage race car, "touring" motor, etc.
As far as what can be done, all the normal speed tricks. High Compression head, bigger valves, boring w/ lighter pistons, cam, multiple carbs/downdraft carbs, header, cutting the flywheel, V8 clutch and pressure plate.
If you really have deep pockets, you can buy an aluminum block, 5 main crank, overhead valve conversion, some fuel other than gas.
I'm sure I left out some things.
Let your conscience be your guide. Good Luck