A turbo is hard to get working with a carb since you cannot pressurise it, you would have to include injection for such a system (not as dramatic as it sounds, specially of you can aqcuire a complete 999-injected donor, together with loom).
Assuming it will stay carbed, the biggest increase can be expected from a bigger/double carb, together with a different cam, and a decent exhaust. If more increase is required, headwork (flowing) would be the next step.
The carb version has a lobe on the camshaft for the mechanical fuel pump, which limits your choice of cams, you could do a regrind or rebuild to electric fuel pump setup (with use of a fuel-return-line)
A lot is possible, and it is easy to make it overly expensive / complicated / riscfull on yourself. It all starts with clear and realistic goals and budgets. The availability and proces of 2nd hand or scrayard items may loosen restrictions a bit.
If you are looking for a small increase in power and get satisfaction in a bit of fiddling with your engine, try to buy a donor engine to start working on, while your runner starts on the road.
If you are looking for a substantial increase, hate dirty hands, or do not have substantial technical knowledge, simply buy a faster car (e.g. something with a 1.2-fire, 1.4-16v fire, or something faster alltogether)
(On the other hand, if you do like the fiddling and learning, the 8v-fire is a bomb-proof, easy, cheap and rewarding subject, with plenty of choice from standard part bins, available at your nearest scrapyard)