If you want to keep it relatively straight forward then there are only 2 real options:
1. Weber 32/26 carburettor, full 2" exhaust (including headers), upgrade camshaft.
2. Replace 20R with 22R engine.
Can also do both options.
Even better if you put the old 20R head on the new 22R block (raises the compression ratio, which allows you to tune for more power).
http://members.iinet.net.au/~stepho/eng20r.htm
Plenty of shops out there do 20/22R work.
eg
www.lcengineering.com
If you do the 22R swap, you can also consider if you want EFI.
Wiring up the EFI computer is not very hard and is otherwise similar to any other 22R swap.
Will need a high pressure fuel pump.
http://members.iinet.net.au/~stepho/celfaq.txt
http://members.iinet.net.au/~stepho/