Definantly solid axle swap. Will probably cost the same as changing your control arms etc, and will be far stronger!
If you want to lift the IFS however, you could try this method
http://www.toyotasurf.asn.au/techsite/customsuspension.htm
if they use the same technology as the Hilux IFS, but i dont think they do.
Other than that, PM bitsamissin about his little gadget "the articulator" which will allow u to isolate the sway bar mechanism giving you far better articulation off road. This coupled with aftermarket torsion bars with tweaking and good shocks will be a good base to start with.
I think big balls offroad sells IFS suspension kits
http://www.bigballsoffroad.com.au which included dropped cross members, longer wishbones, brakelines, torsion bars etc, but they were over the $3k mark.
happy hunting
