Ok, well i was going to say factor on about $1000 for a basic rebuild with flat tops, forgies will cost about $1000 on top of that.
Get some minor portwork done around the bowls(about 400 more) and a mid sized cam.
Balancing is a good idea on the old Lseries, they are a rough old motor at the best of times.
As far as fuel supply goes, a set of webers is ideal but SU's(or CD strombergs) will suffice, failing these carb setups an old weber off a falcon isnt a bad little upgrade, but the inlet manifold will restrict you....maybe a 280C manifold will be larger, i never tried it.
A set of extractors and a 2.5in exhaust will have the whole package sounding tough and going quite well too.
Manual Conversion List:
Manual box(duh)
clutch pedal and all springs/pivots/clips
clutch master cylinder
master to slave pipe
slave cylinder
spigot bush(for in the end of the crankshaft....12 bucks i thinks from nissan)
flywheel
mmmmmm....i think thats all
if you are going to do this yourself, don't forget to pull the cap off the end of the crankshaft, or your flywheel wont fit.
cheers, jason