Ok for my opinion,
G-series (Hilux), its what I run in my 1200 Race car.
If you are never going to see the road, look to run floater hubs. This is safer for drag/circuit racing and much easier to do as an alternative to shortening. This prevents the wheel coming off when you snap an axle. Can also camber the rear.
http://msfracingcomponents.com.au/fullfloatinghubkits/ is a good start.
If you are drag racing then the standard Toyota LSD should be fine. Bolt in upgrade is a Cusco. Kaaz requires a ring gear spacer to fit. cheaper options (non ramped) are Loka's which would work well for drag racing. or for a cheap option Spool (full, mini, GIC).
Remember when you replace the rear suspension or convert to 4 link, consider how the thing will roll and act under acceleration, braking (anti's - Dive/Squat), there is an art to getting up the rear properly and not just weld 4 equal length rods in and call it a 4 link.

Hope that helps, good luck

Bryan