Lots of things you can do and depends on your countries limits laws etc.
do you want all out power or just good torque for daily use?

All out power you cannot go past boost with SU carb.

for just extra oomph and Torque you need good ignition and the mentioned above goodies

Massive torque and driveability without sky high revs.

You will need a custom Headgasket made for full sleeved block
like renault 5 to 83mm using milled tops on ca18de pistons,
mild cam, ignition, headers and IDA single 36mm carb should
be a stump puller with big valve head and ported inlet mani.
1775cc but youll need deep pockets and gearbox to suit.