I would say go with a Webber carbie. The standard one is very restrictive. That is the easiest power upgrade right now. THen you can get a different cam shaft with longer duration, and stiffer valve springs to use a higher rev range.
If you have points in the distributor, you want to change them very regulary, or even convert to electronic ignition. Get a electronic distributor off a import 4K or 5K motor with matching coil and igniter.
You can use regular unleaded. With higher octane fuel you can advance the ignition a little more.
I surgest you buy a strobe light thing yourself and learn to use it. For basic engine stuff, a workshop manual is better than unqualified advice on the internet.